Post on 28-Dec-2015
1
Organic LEDs ndash part 8
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 20b
2
Exciton Dynamics in Time Dependant PL
3
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 ]
4
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
5
Electronic Processes in Molecules
density of availableS1 or T1 states
6
Time Evolution of DCM2 Solution PL Spectra
7
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
8
Excitonic Energy Variations
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
2
Exciton Dynamics in Time Dependant PL
3
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 ]
4
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
5
Electronic Processes in Molecules
density of availableS1 or T1 states
6
Time Evolution of DCM2 Solution PL Spectra
7
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
8
Excitonic Energy Variations
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
3
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 ]
4
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
5
Electronic Processes in Molecules
density of availableS1 or T1 states
6
Time Evolution of DCM2 Solution PL Spectra
7
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
8
Excitonic Energy Variations
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
4
Time Evolution of 4 DCM2 in Alq3 PL Spectrum
5
Electronic Processes in Molecules
density of availableS1 or T1 states
6
Time Evolution of DCM2 Solution PL Spectra
7
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
8
Excitonic Energy Variations
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
5
Electronic Processes in Molecules
density of availableS1 or T1 states
6
Time Evolution of DCM2 Solution PL Spectra
7
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
8
Excitonic Energy Variations
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
6
Time Evolution of DCM2 Solution PL Spectra
7
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
8
Excitonic Energy Variations
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
7
Spectral Shift due to
~ Exciton Diffusion ~~ Intermolecular Solid State Interactions
~
8
Excitonic Energy Variations
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
8
Excitonic Energy Variations
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
9
Exciton Distribution in the Excited State (S1 or T1)
~ Time Evolved Exciton Thermalization ~
EXCITON DIFFUSION LEADS TO REDUCTION IN FWHM
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
10
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
11
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
12
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
13
Time Evolution of Peak PL in Neat Thin Films
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
14
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))
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
15
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
16
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
17
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)
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
18
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)
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
19
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
20
Inorganic Nanocrystals ndash Quantum Dots
Quantum Dot SIZE
Synthetic route of Murrayet al J Am Chem Soc115 8706 (1993)
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
21
Fusion of Two Material Sets
Quantum Dots Organic Molecules
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
22
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
23
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
24
As the concentration ofQDs in the spin-castingsolution is increasedthe coverage of QDs onthe monolayer is alsoincreased
Monolayer Coverage ndash QD concentration
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
25
CdSe(ZnS)TOPO PbSeoleic acid
QD-LED Performance
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
26
Full Size Series of PbSe Nanocrystals
from 3 nm to 10 nm in Diameter
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
27
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
28
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
29
EL RecombinationRegion Dependence
on Current
Coe et al Org Elect (2003)
30
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
31
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
30
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
31
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
31
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