Quantum Dots for Conversion of

Electricity to Light

Paul H. Holloway, Jake Hyvonen, Alexandre Titov,

Jean Tokarz-Scott and Krishna P. Acharya

Research Park, Alachua FL

What Are Quantum Dots?

Schapotschnikow et al J Phys Chem C 113 (2009)

~3-15nm

Core/shell QD

Shell passivates inorganically

Shell creates heterostructure

Size-dependent properties

http://www.photonics.com/images/spectra/features/2007/May/QuantumDots_Fig5_

CoreShell.jpg

Core

Shell

Ligands

h+

e-

aBohr

Exciton Exciton 𝑎𝐵 =

4𝜋𝜖𝑜𝜖𝑟ℏ2

𝑒21

𝑚𝑒∗ +

1

𝑚ℎ∗

NanoPhotonica • Core/Intermediate Zone/Shell

• Continuous composition gradient

• Composition/size/color; 6-8 nm

• Ligand exchange

Advantages of QDs and QLEDs

1. Large Area

i. Distributed light sources for SSL

ii. Large screen size for displays possible

2. Low manufacturing cost by Inkjet or similar solution

processing

3. Low raw materials cost – mostly abundant elements

4. Thin, Light, Flexible and Transparent Form Factors

5. Most pure colors available without lasers

• All solution processable quantum dot light-emitting diode (QLED)

• Solvent orthogonality enables multilayered structure

• Good charge confinement in QD

• Good electron injection from ZnO NPs

TRANSPARENT SUBSTRATE

ITO ANODE

HOLE INJECTION LAYER

HOLE TRANSPORT LAYER

CORE-SHELL QD LAYER

ZnO NANOPARTICLE ETL

Al CATHODE

Our Solution: Improved Materials and Device

400 500 600 700 800

Ele

ctr

olu

min

es

ce

nc

e (

a.u

.)

Wavelength (nm)

QLED Optoelectronic Characteristics

0 1 2 3 4 5 6 710

-9

10-7

10-5

10-3

10-1

101

103

Cu

rren

t D

en

sit

y (

mA

/cm

2)

Voltage (V)

10-3

10-1

101

103

105

107

109

1011

Lu

min

an

ce (

cd

/m2)

FWHM (nm)

Color λmax

(nm)

FWHM

(nm)

EQE (%) P.E. (lm/W) C.E. (cd/A)

Peak Peak Peak

Blue 463 24 12.3 6.0 8.1

Green* 526 27 21-limit 79.8 82

Red 631 27 13.8 18.3 14.3

Manders et al., Distinguished Paper, JSID, 46, 73–75, June 2015 DOI: 10.1002/jsid.393

6

1 10

10-3

10-2

10-1

100

101

102

103

104

3 nm ZnO NPs

5 nm ZnO NPs

Sol-gel ZnO

E-beam ZnO

L (

cd

/m2)

V (V)

ZnO Size Effect

• Increased EQE, current & power efficiency with

time

– Increase EQE from 1% up to 10%; similar range for ηc, ηp

– First accomplished with UV cured epoxy encapsulated device stored in glove box (up to 6-30 days; varies with many parameters)

– Due to a fortuitous interaction with the encapsulant

– Patent pending

– Efficiency is not limiting applications

7

Positive Aging

8

Positive Aging Effect – Typical Good Device

0 1 2 3 4 5

1E-3

0.01

0.1

1

10

100

1000

10000

Lu

min

ance

(cd/m

2)

Voltage (V)

Day 1

Day 4

Day 7

450 500 550 600

0.0

0.2

0.4

0.6

0.8

1.0

Inten

sit

y (

a.u

.)Wavelength (nm)

Day 4 Day 7

9

-200 0 200 400 600 800 1000 1200 1400 1600

2.0

2.5

3.0

3.5

4.0

4.5

5.0 Voltage

Luminance

Time (hrs)

Vol

tage

(V)

700

800

900

1000

1100

1200

1300

1400

1500

Lum

inan

ce (c

d/m

2 )

Red QLED Life Test T75 = 1400 hrs @ 1200 nits; T75 = 2200 hrs @ 900 nits;

T75 = 180,000 hrs @ 100 nits

T75

Artefact

Pure Colors Advantage

Color advantages of QLED:

1. Wider color gamut – broad CIE color coordinates

2. >170% NTSC, ~90% Rec. 2020

OLED Gamut

Manders et al., JSID. Accepted (2015) DOI: 10.1002/jsid.393

NanoPhotonica has demonstrated:

• QLED performance comparable to OLED properties

• Simple, low cost solution processed QLED structures

• EQE > 10% achieved for all three colors at high brightness

(100-10000 nits)

• Simple encapsulation process improves efficiencies; not

limiting

• R,G, B lifetimes are limiting

• Color purity, high efficiency, low cost solution processing:

NEXT GENERATION TECHNOLOGY

11

Summary