Organic LEDs ndash part 7

bull Solvation Effect ndash Review

bull Solid State Solvation

bull Exciton Dynamics in Disordered Organic Thin Films

bull Quantum Dot LEDs

Handout on QD-LEDs Coe et al Nature 420 800 (2002)

April 29 2003 ndash Organic Optoelectronics - Lecture 20

Electroluminescence in Doped Organic Films

1Excitons formed

from combinationof electrons and

holes

2Excitons transfer to

luminescent dye

Electroluminescence of x DCM2 in Alq3 OLEDs

1048790 solvation is a physical perturbation of lumophorersquos molecular states1048790 isolated molecule (in a gas phase) and solvated molecule are in the same chemical state(no solvent induced proton or electron transfer ionization complexation isomerization)

change in the spectral position of aborption luminescence band

due to change in the polarity of the medium

Solid State Solvation (SSS)

polarlumophor

e

dipolar hostwith moment μ

ldquoself polarizationrdquofor strongly dipolar lumophores

(aggregation possible for highly polar molecules)

solute (chromophore)WITH DIPOLE MOMENT μ

solvent

Bathochromic (red) PL shiftHypsochromic (blue) PL shift

Influence of μ0 and μ1

on Chromatic Shift Direction

PL of DCM2 Solutions and Thin Film

Bulović et al Chem Phys Lett 287 455 (1998)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-equilibrium)

Dynamic Relaxation Picture (aka solvation)

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Electroluminescence in Doped Organic Films

1Excitons formed

from combinationof electrons and

holes

2Excitons transfer to

luminescent dye

Electroluminescence of x DCM2 in Alq3 OLEDs

1048790 solvation is a physical perturbation of lumophorersquos molecular states1048790 isolated molecule (in a gas phase) and solvated molecule are in the same chemical state(no solvent induced proton or electron transfer ionization complexation isomerization)

change in the spectral position of aborption luminescence band

due to change in the polarity of the medium

Solid State Solvation (SSS)

polarlumophor

e

dipolar hostwith moment μ

ldquoself polarizationrdquofor strongly dipolar lumophores

(aggregation possible for highly polar molecules)

solute (chromophore)WITH DIPOLE MOMENT μ

solvent

Bathochromic (red) PL shiftHypsochromic (blue) PL shift

Influence of μ0 and μ1

on Chromatic Shift Direction

PL of DCM2 Solutions and Thin Film

Bulović et al Chem Phys Lett 287 455 (1998)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-equilibrium)

Dynamic Relaxation Picture (aka solvation)

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Electroluminescence of x DCM2 in Alq3 OLEDs

1048790 solvation is a physical perturbation of lumophorersquos molecular states1048790 isolated molecule (in a gas phase) and solvated molecule are in the same chemical state(no solvent induced proton or electron transfer ionization complexation isomerization)

change in the spectral position of aborption luminescence band

due to change in the polarity of the medium

Solid State Solvation (SSS)

polarlumophor

e

dipolar hostwith moment μ

ldquoself polarizationrdquofor strongly dipolar lumophores

(aggregation possible for highly polar molecules)

solute (chromophore)WITH DIPOLE MOMENT μ

solvent

Bathochromic (red) PL shiftHypsochromic (blue) PL shift

Influence of μ0 and μ1

on Chromatic Shift Direction

PL of DCM2 Solutions and Thin Film

Bulović et al Chem Phys Lett 287 455 (1998)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-equilibrium)

Dynamic Relaxation Picture (aka solvation)

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

1048790 solvation is a physical perturbation of lumophorersquos molecular states1048790 isolated molecule (in a gas phase) and solvated molecule are in the same chemical state(no solvent induced proton or electron transfer ionization complexation isomerization)

change in the spectral position of aborption luminescence band

due to change in the polarity of the medium

Solid State Solvation (SSS)

polarlumophor

e

dipolar hostwith moment μ

ldquoself polarizationrdquofor strongly dipolar lumophores

(aggregation possible for highly polar molecules)

solute (chromophore)WITH DIPOLE MOMENT μ

solvent

Bathochromic (red) PL shiftHypsochromic (blue) PL shift

Influence of μ0 and μ1

on Chromatic Shift Direction

PL of DCM2 Solutions and Thin Film

Bulović et al Chem Phys Lett 287 455 (1998)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-equilibrium)

Dynamic Relaxation Picture (aka solvation)

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Solid State Solvation (SSS)

polarlumophor

e

dipolar hostwith moment μ

ldquoself polarizationrdquofor strongly dipolar lumophores

(aggregation possible for highly polar molecules)

solute (chromophore)WITH DIPOLE MOMENT μ

solvent

Bathochromic (red) PL shiftHypsochromic (blue) PL shift

Influence of μ0 and μ1

on Chromatic Shift Direction

PL of DCM2 Solutions and Thin Film

Bulović et al Chem Phys Lett 287 455 (1998)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-equilibrium)

Dynamic Relaxation Picture (aka solvation)

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

solute (chromophore)WITH DIPOLE MOMENT μ

solvent

Bathochromic (red) PL shiftHypsochromic (blue) PL shift

Influence of μ0 and μ1

on Chromatic Shift Direction

PL of DCM2 Solutions and Thin Film

Bulović et al Chem Phys Lett 287 455 (1998)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-equilibrium)

Dynamic Relaxation Picture (aka solvation)

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

PL of DCM2 Solutions and Thin Film

Bulović et al Chem Phys Lett 287 455 (1998)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-equilibrium)

Dynamic Relaxation Picture (aka solvation)

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-equilibrium)

Dynamic Relaxation Picture (aka solvation)

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

1 DCM2 in Alq3

1 DCM2 in Zrq4

polar hostμ ~ 55 D

non-polar host

Thin Film Photoluminescence

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

A ldquoCleanerrdquo Experiment

bull Employ trace DCM2 so as to effectively eliminate aggregation

bull But still appreciably change local medium use rArr another dopant

bull should be polar and optically inactive (ie wide band gap)

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

CA Doping and Electronic Susceptibility

42 nm red shift from 0 to 25 CA

Results unchanged even for 10x

higher DCM2 concentration

DCM2 aggregation not the answer

Local fields are responsible for thespectral shiftshellip

hellip and dielectric measurementssuggest a ldquosolvatochromicrdquo effect

Peak PL Energy of PSCADCM2 Films

Bulk Electronic Susceptibility of PSCADCM2 Films

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Solvation TheoryDynamic Relaxation Picture (aka solvation)

Excited State(non-

equilibrium)

Excited State(equilibrium)

Ground State(equilibrium)

Ground State(non-

equilibrium)

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Connecting Theory to Experiment

constant with CA n nearly constant with CA(ranging from ~155 to ~165)

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Exciton Dynamics in Time Dependant PL

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Dynamic Spectral Shifts of DCM2 in Alq3

bull Measurement performed on doped DCM2Alq3 filmsbull Excitation at λ=490 nm (only DCM2 absorbs)

~ DCM2 PL red shifts gt 20 nm over 6 ns ~

Wavelength [ nm ]

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Time Evolution of 4 DCM2 in Alq3 PL Spectrum

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Electronic Processes in Molecules

density of availableS1 or T1 states

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Time Evolution of DCM2 Solution PL Spectra

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Spectral Shift due to

~ Exciton Diffusion ~~ Intermolecular Solid State Interactions

~

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Excitonic Energy Variations

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Exciton Thermalization ~

EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Time Evolution of Peak PL in Neat Thin Films

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Parameters for Simulating Exciton Diffusion

observed radiative lifetime (τ)No

rmal

ized

Inte

grat

ed Sp

ectr

al In

tens

ity

Foumlrster radius (RF) Assign value for allowed transfers

Assume Gaussian shape of width wDOS

Center at peak of initial bulk PL spectrum Molecular PL spectrum impliedhellip

excitonic density of states (gex(E))

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Fitting Simulation to Experiment ndash Doped Films

bull Good fits possible for all data sets

bull RF decreases with increasing doping falling from 52 Aring to 22 Aring

bull wDOS also decreases with increasing doping ranging from 0146 eV to 0120 eV

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
• Slide 21
• Slide 22
• Slide 23
• Slide 24
• Slide 25
• Slide 26
• Slide 27
• Slide 28
• Slide 29
• Slide 30
• Slide 31
• Slide 32
• Slide 33
• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Fitting Simulation ndash Neat Films

bull Spectral shift observed in each material system

bull Molecular dipole and wDOS are correllated lower dipoles correspond to less dispersion

bull Even with no dipole some dispersion exists

bull Experimental technique general and yields firstmeasurements of excitonic energy dispersionin amorphous organic solids

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
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• Slide 44

Temporal Solid State Solvation

upon excitation both magnitude and direction

of lumophore dipole moment can change

FOR EXAMPLE for DCM micro1 ndash micro0 gt 20 Debye ~ from 56 D to 263 D ~

following the excitation the environment surrounding the

excited molecule will reorganize to minimize the overall

energy of the system (maximize micro bull Eloc)

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 36
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• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Exciton Distribution in the Excited State (S1 or T1)

~ Time Evolved Molecular Reconfiguration ~

DIPOLE-DIPOLE INTERACTIONLEADS TO ENERGY SHIFT IN DENSITY OF EXCITED STATES

log(Time)

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Fusion of Two Material Sets Hybrid devicescould enable

LEDs Solar CellsPhotodetectorsModulators and

Lasers

which utilize thebest properties of each individual material

Efficient

OrganicSemiconductors

Flexible

Emissive

Fabrication ofrational

structureshas been the

mainobstacle to date

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
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• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Inorganic Nanocrystals ndash Quantum Dots

Quantum Dot SIZE

Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Fusion of Two Material Sets

Quantum Dots Organic Molecules

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
• Slide 14
• Slide 15
• Slide 16
• Slide 17
• Slide 18
• Slide 19
• Slide 20
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• Slide 22
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• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Integration of Nanoscale MaterialsQuantum Dots and Organic Semiconductors

ZnS overcoating shell(0 to 5 monolayers)

Oleic Acid orTOPO capsSynthetic routes of Murray et

al J Am Chem Soc 1158706 (1993) and Chen et alMRS Symp Proc 691G102

Trioctylphosphine oxide

Tris(8-hydroxyquinoline)Aluminum (III)

3-(4-Biphenylyl)-4-phenyl-5-tert-butylphenyl-124-triazole

NN-Bis(naphthalen-1-yl)-NN-bis(phenyl)benzidine

NN-Bis(3-methylphenyl)-NN-bis-(phenyl)-benzidine

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
• Slide 12
• Slide 13
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• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

1 A solution of an organic material QDs and solventhellip2 is spin-coated onto a clean substrate3 During the solvent drying time the QDs rise to the surfacehellip4 and self-assemble into grains of hexagonally close packed spheres

Organic hosts that deposit as flat filmsallow for imaging via AFM despite theAFM tip being as large as the QDs

Phase segregation is driven by acombination of size and

chemistry

Phase Segregation and Self-Assembly

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
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• Slide 43
• Slide 44

As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased

Monolayer Coverage ndash QD concentration

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

CdSe(ZnS)TOPO PbSeoleic acid

QD-LED Performance

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Full Size Series of PbSe Nanocrystals

from 3 nm to 10 nm in Diameter

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 34
• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Design of Device StructuresQDs are poor chargetransport materials

Isolate layer functions of maximizedevice performance1 Generate excitons on organic

sites2 Transfer excitons to QDs via Foumlrster or Dexter energy transfer3 QD electroluminescence

Phase Segregation

But efficient emittershellip

Use organics for charge transport

Need a new fabrication method inorder to be able to make such doubleheterostructures

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
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• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

A general method

Phase segregation occurs for different

1) organic hosts TPDNPD and poly-TPD

2) solvents chloroformchlorobenzene andmixtures with toluene

3) QD core materialsPbSe CdSe andCdSe(ZnS)

4) QD capping moleculesoleic acid and TOPO

5) QD core size 4-8nm

6) substrates SiliconGlass ITO

7) Spin parametersspeed accelerationand time

bull This process is robust but further exploration is needed to broadly generalize these findingsbull For the explored materials consistent description is possiblebull We have shown that the process is not dependent on any one material componentPhase segregation 1048774 QD-LED structures

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
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• Slide 41
• Slide 42
• Slide 43
• Slide 44

EL RecombinationRegion Dependence

on Current

Coe et al Org Elect (2003)

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 38
• Slide 39
• Slide 40
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• Slide 42
• Slide 43
• Slide 44

Spectral Dependence on Current Density

TOP DOWN VIEW of the QD MONOLAYER

Exciton recombinationwidth far exceeds the QDmonolayer thickness athigh current densityTo achieve truemonochrome emissionnew exciton confinementtechniques are needed

CROSS-SECTIONAL VIEW of QD-LED

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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• Slide 35
• Slide 36
• Slide 37
• Slide 38
• Slide 39
• Slide 40
• Slide 41
• Slide 42
• Slide 43
• Slide 44

Benefits of Quantum Dots in Organic LEDs

Demonstrated bullSpectrally Tunable ndash single material set can access most of visible range bullSaturated Color ndash linewidths of lt 35nm Full Width at Half of Maximum bullCan easily tailor ldquoexternalrdquo chemistry without affecting emitting core bullCan generate large area infrared sourcesPotential bullHigh luminous efficiency LEDs

possible even in red and blue bullInorganic ndash potentially more stable longer lifetimes

The ideal dye molecule

• Slide 1
• Slide 2
• Slide 3
• Slide 4
• Slide 5
• Slide 6
• Slide 7
• Slide 8
• Slide 9
• Slide 10
• Slide 11
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