White Organic Light Emitting Diodes for Super-thin Flat Panel Lighting

Taiju Tsuboi

Kyoto Sangyo University, Kyoto, Japan

FNMA09 L’Aquila-Sulmona, September 28, 2009

Outline

1.Why white OLED is necessary for lighting ?

2. What is OLED ?

3. How to make white OLEDs ?

electricity consumption in Japanese houseselectricity consumption in Japanese houseselectricity consumption in Japanese houseselectricity consumption in Japanese houses

29%

4%10%

16%

16%

25%

Japanese Government report Japanese Government report Japanese Government report Japanese Government report

Air-conditionrefrigerator

lighting

TV heating

others

Why OLED lighting and OLED displays are needed ?

Because of Shortage of Oil Resource

No more oil after 40 years ?

Pro

du

ctio

n o

f O

il

Low-energy consuming lighting and display are needed.

Power efficiency of lighting

power efficiency: η = η = η = η = ππππL(cd)/J(A)V(V)

Incandescent lamp(100W)：：：： 16～～～～18 lm/WXe lamp ：　　　　　：　　　　　：　　　　　：　　　　　 25～～～～35 lm/W

Fluorescent lamp:　　　　 40～～～～110 lm/W

White LED (Cree, USA)：：：： 131 lm/W

White LED (Nichia, Japan)：：：： 150 lm/W

White OLED (Universal Display Corp., USA) ：：：：102 lm/W (2008.6.) at1000cd/m2

White OLED (Novaled AG, Germany)：：：：90 lm/W at 1000cd/m2 ,

with attachment 124 lm/W (2009.5.)

Problems:

LED: shortage of rare metals like In and Ga

Fluorescent lamp ：　containing Hg

Organic Electronics

Displays

Electronic paper

Transistor, Condenser

Solar cell

Lasers : Easily tunable and any emitting color

New Lighting using white OLED

Everything by organic materials

General Electric Global

Research Co.Fraunhofer Institut für Photonische

Mikrosysteme (IPMS) in Dresden OSRAM

Progress of TV displays

CRT-TV

Liquid Crystal DisplayPlasma Display Panel

Organic Light emitting diode (OLED) display

Thickness: 3 mm

Consumption power: 45 V

Contrast: 1,000,000:1

SONY OLED 11’ TV「「「「XEL-1」」」」Dec., 2007

Contrast: 3,000 : 1 Contrast: 8,000 : 1

Principle of LC Display

bright

dark

Orientation of LC is changed by applied voltage

polarizer

E(=V/d)

polarizer

No light

Nematice liquid crystal

Electric field plane of light

V=0

V

1.Self-emission, No back-light

2.High response, wide viewing angle

3.High contrast image

4.Super-thin flat, lightweight

5.Flexible, paper-like display

6.Low voltage operation 5V: Low cost operation

7.Organic materials: Easy manufacturing

8. Low cost for production

Advantage of OLED devices

Universal Display Corp. Fraunhofer Institut für Photonische

Mikrosysteme (IPMS) in Dresden OSRAM

Metal cathodeMetal cathode

　　　　　　　　

　　　　　　　　- - - - - - -

transparent transparent 　　　　　　　　ITO anodeITO anode

Glass plateGlass plate

+++++++

Emission by Recombination of electron and

hole : Electroluminescence

3-7V

Organic Light Emitting Diode　(OLED)　with organic semiconductors

0.4µm

hole transporthole transport

layerlayer

Electron Electron

Transport layerTransport layer

emittinemittinｇ　ｇ　ｇ　ｇ　ｇ　ｇ　ｇ　ｇ　layerlayer

Inorganic LED

ｎｎｎｎ型型型型

ｐｐｐｐ型型型型

-

＋＋＋＋

＋＋＋＋

-

hole

electroncrystal

Kyoto Sangyo Univ. Kyoto Sangyo Univ.

Green and Red OLEDs White OLEDs

Actual OLED with multi-layersfor carrier balance and confinement

to make high density excitons

NPD

PtOEP

BAlq

Alq

ITO

LiF/Al

5.0

1.9eV

5.2eV

2.9

5.3

2.76

5.9

2.8

5.41

2.9eV－

＋

＋－

EL

Transparent Anode

α-NPD

ITO

LiF

Glass Substrate

Ir(ppy)3 : CBP

BCPAlq3

Al

excitons

0.320.320.320.32µµµµm

Cathode

Electron injection

layerETL

Emission layer

HTL

Hole injection layer

Anode----ITO glass substrate

Electroluminescence EL

　　　　emitter is doped in host emitter is doped in host emitter is doped in host emitter is doped in host e.g. green e.g. green e.g. green e.g. green IrIrIrIr((((ppyppyppyppy))))3333 in CBP, in CBP, in CBP, in CBP,

red red red red PtOEPPtOEPPtOEPPtOEP in CBP, in CBP, in CBP, in CBP,

red DCM1 in Alqred DCM1 in Alqred DCM1 in Alqred DCM1 in Alq3333

Guest-Host system

HOMO

LUMO

confinement electrons and holes in emitting layer

CuPc

αααα－－－－NPD

Ir(ppy)３３３３

in CBP

BCPAlq３３３３ITO

Al

4.7eV 5.025.46

5.52

6.45.7

4.2

3.09

2.452.7

2.93.0

－ － －

－

＋

＋＋＋

Hole transport layer

Electron blocking layer

Hole blocking layer

LUMO

HOMO

electron

Electron transport layer

Hole injection layer

Electron injection layer

Emitting layer

Emission by e-h recombination

LUMO

HOMO

hopping

hoppingITOAl

carrier hopping in HOMO and LUMO levels in amorphous semiconductor film

ITOanode

5.0eV

dopanthost

LUMO

HOMO

exciton

Molecular states

of dopant

hole

electron

hole and then electron

are trapped at dopant

CBP

5.52eV

2.9eV

Ir(ppy)3

5.1eV

2.9eV

Al/LiF cathode

1.89eV

CBP

123

23

＋＋＋＋

ーーーー

N： (1s)2(2s)2(2p)3

Removal of electron from hole

transport molecules α－NPD

1

2

hopping

hopping

Cathode Anode

Electron Hole

Conduction Band(LUMO)

Valence Band(HOMO)

Electron-Hole Capture; Exciton

Singlet Exciton Triplet Exciton

Light Emission Heat Dissipation

Light Output Internal Decay

ηηηηout

Scheme of EL Process

γγγγ

ηηηηex

ηηηηr

How to increase the quantum efficiency in OLED ?

Cathode

Electron

injection layerETL

Emission layer

HTL

Hole injection

layerAnode----ITO glass

substrate

1. High numbers of injected electrons and

holes in emitting layergood injection layer

high carrier mobility materials

confinement of electrons and holes

2. Same number of electrons and holesbecause exciton is formed by e+h

3. All excitons should be used for emissionPhosphorescent emitter is the best.

4. Emission should be taken outside from emitting layer inside of OLED efficiently

Electroluminescence spectra

400 450 500 550 600 650 700 7500.00

0.01

0.02 Ir1Ir(ppy)

3Pt2PtOEP

em

issio

n in

ten

sity (

arb

. u

nits)

wavelength (nm)

Ir(ppy)3 PtOEP(Platinum

octaethylporphyrin)tris(2-phenylpyridine) iridium

Mono color white color

400 450 500 550 600 650 700 7500.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

ele

ctr

olu

min

esce

nce

(a

rb.

un

its)

wavelength (nm )

at 5 V

red

blueWhite OLED

Fujitsu

Feb., 2004　　May, 2004

Main LCD　　　　262,144 colors 2.4“TFT

Front OLED　　　　　　　　4,096 colors 1.1“

F506iF900i

Cellar phone with OLEDs Kodak Digital Camera

LS433　LCD　　　 LS633 OLED　

Currently available OLED displays

Kodak One-Seg OLED TV

SAMSUNG AMOLED TL320 Digital camera

12.2 Mega Pixels

Currently used OLED display

Matsushita Co.,

Victor Co. Audio compoPioneer Co., Display panel for automobiles

Sony

Olympus

portable audio player

What lighting is good for us ?

usual f. lamp CRI CRI CRI CRI 60606060

3-λ f. lmap　CRI CRI CRI CRI 80808080

3-λ naturalf.lmap CRI CRI CRI CRI 90909090 http://map.answerbox.net/landmark-368647-bbs-2.htm

Materials should be seen under lighting just as seen under sun.

White light as sunshineCRI　color rendering index　 under sunshine CRI=100 (standard)

　　　　　　　　 color temperature: 2500-6000K　　　　　　　　chromaticity index CIE　　　　(0.33, 0.33)　　　　

　　　　CRI＞＞＞＞80

sunlight

generation of white light

D.　Tandem structure

C.Color conversion: B to G, B to R

B. White with

RGB color filters

A.　RBG parallel

E.　Single emitting layer

Grass substrate

ITO

NPD(60nm)

EML

BAlq(20nm)

Alq3　(55nm)

Al

R,B emission

R,G,B emission

2-color B+G WOLED

Y.S. Wu et al, Thin Solid Films 488(2005)265.

DSA-ph TBRb

Device A is much better than Device B.

B

B

G

G

A

B

B

A

青色

オレンジ

3-layer emission due to Bepp2, Alq3, Rubrene

Z.Y. Xie et al, APL, 74(1999) 641

3-Layer emission

Zhu, Li, Tsuboi, et al, Opt. Lett. 32(2007) 3537.

CIE = (0.33, 0.33)

CCT(correlated color Temp.)= 2500-6000 K

CRI(color rendering index) > 80

High external efficiency from POLED with three small

molecules

WOLED1 ; 16.6 %

WOLED2; 6.0%

FIr6: bis(40,60-difluorophenylpyridinato) tetrakis(1-pyrazolyl)borate

PQIr: Ir(III) bis(2-phenylquinolyl-N,C20) acetylacetonate

Y. Sun, S.R. Forrest, Org. Electron.9 (2008) 994.

Reducing hole mobility for charge balance, Uniform

distribution of holes and electron.

Ambipolar host for uniform exciton formation across

the entire EML

OLEDs with Exciplex emission

Exciplex emission

D. Wang, W.L.Li, T. Tsuboi et al, APL 92(2008)053304.

4,4’,4”-tris[3-methylpheny-l(phenyl)amino] triphenylamine (m-MTDATA): hole-transport material :

M ���� M+ + e

4,7 dipheny-1,10-phenanthroline (Bphen): electron-transport material : B + e ���� B-

M+ + B-����(MB)* ���� MB + hνννν

emission from interface

B-

M+

6620cd/m2 at 8.7V

monomer

donoracceptor

250 300 350 400 450 5000.0

0.1

0.2

0.3

0.4

0.5

0.6

op

tica

l d

en

sity

wavelength (nm)

m-MTDATA

BPhen

BPhen+m-MTDATA(1:1)

No emission from Bphen monomer

White OLED with exciplex and monomer

2000 cd/m2

0.58 lm/W

CIE (0.31,0.35)

J. Feng et al, APL78 (2001) 3947.

monomer exciplex

White OLED using only exciplex

Monomer

emission

Exciplex emission

EL

J.Z. Zhu, W.L. Li, T. Tsuboi, et al,

to be published.

Very wide broad band

Al(DBM)

m-MTDATATPD

Bphen

Four exciplexes in a device

Intralayer exciplex

boundary exciplex

donor

acceptor

m-MTDATA

R=M-MTDATA:Al(DBM)3

Increase of Intralayer exciplex

Decrease of R:

Decrease of m-MTDATA

Decrease of red exciplex

Multi-coloration by single molecule

Excimer

Mixed ligand molecule

Single dopant WOLED

with Excimer emission

M*M M + M + hυexcimer

*T. Tsuzuki, S. Tokito, Proc. Int. Super-FunctionalityOrganic Devices, IPAP Conf. Series 6 (2005) 99.

FPｔ

excimer

FPt monomer

Pt compounds: plane structure, stacking

N^C^NN^C^NN^C^NN^C^N----Pt(Pt(Pt(Pt(ClClClCl))))

cyclometalated Pt2+-compounds

QE= 6.1% , CRI=73, CIE=(0.32, 0.39), 11.8 lm/W (at 1cd/m2)

V. Adamovich et al, New J. Chem. 26 (2002) 1171.

polymer or small molecule ?

Polymer:

spin-coating, wet-process: cheap, easy, simple

structure (2-layer), and ink-jet possible (for mass-

production)

Small molecule:

thermal evaporation in high vacuum, dry process: high

cost

Polymer White OLEDs

dopant host emitter

FL small molecule FL polymer Dopant

PL small molecule FL polymer Dopant

FL polymer FL polymer Dopant

PL polymer FL polymer Dopant+host

A. Dispersion type （doping, blend, guest-host）

PL polymer PL polymer Dopnat+host

B. Single polymer

emitter

Non-copolymer Monomer+Excimer FL polymer

Non-copolymer Monomer+Electromer FL polymer

Blended in backbone,

copolymer

Monomer PL polymer

Blended in side-chain,

copolymer

Monomer PL polymer

FL: Fluorescent

PL: Phosphorescent

Guest polymer ＋＋＋＋ host polymer

0.05wt% PPDB（polyperiren-ethylbenzen)dopant

m-LPPP(ladder-type paraphenyrene)　host

Ext. Effic: 1.2　%,

CIE(0.31, 0.33)

PL,PPDBEL,　M-LPPP

M-LPPPPPDB

ITO/ 0.05%PPDB:m-LPPP /Al

S. Tasch et al, APL 71(1997)2883.

Doped WPLED: Polymer-doped polymer

F.Z. Shen et al, Semicon. Sci. Technol. 21(2006)L16.

ITO/PEDOT/0.6wt%MEH-PPV:PF/Ba/Al

PL

host

Ext. Effic: 0.95 %

host

guest

Carrier balanced green polymer

TPD as HT

PBD as ET

Ir(ppy)2(acac) as EL

TPD:PBD:Ir(ppy)2(acac)=

(A)55:41:4, (B)36:62:4, (C)18:79:3

PL

ηext=11.8% at 0.12mA/cm2, power effi.= 38.6 lm/W at 0.02mA/cm2

with Cs e-injector

c.f. S. Lamansky et al, JACS123(‘01)4304:

Ir(ppy)2(acac) in CBP host, multi-layer

OLED

12.3%, 38 lm/W, >50 Cd/A

M. Suzuki (NHK)　et al, APL 86(2005)103507

濃度比が重要

Guest-Host system or Non-doped system ?

White OLEDsETL

HTL

ETL

HTL

Non-dopant system is much better than guest-host system

Because

　 1. Best concentration is 1-2% dopant, difficult to control it

within ±0.5% in mass produced OLEDs

　 2. For White OLED, blue-green-red stacking layered OLED

gives rise to energy transfer from blue to green to red layer、color instability

Single polymer WOLEDs

Backbone copolymer

Side-chain copolymer

monomer Excimer

Electromer

＊

Mono-dopant polymer

polymer

Single backbone copolymer C.Y. Chuang et al, Macromol.40(2007)247

PF:Polyfluoren,

a bipolar charge-tranporting PF derivative

単一高分子型

J. Liu et al, Adv. Func. Mat. 16(2006)957.

BPFB-BT-3

BPF-BT-3

Different dopant:

red-emitter2,1,3-benzothiadiazole-

incorporated blue-polymer

8.99cd/A, 5.75lm/W, ηηηη=3.8%c.f. 3.8cd/A, 2.0lm/W, η=1.50%

backbone copolymer D.Ma

FL+PL

赤色発光：　フェニルキノリンIr錯体Phq燐光分子緑色発光：　ベンゾチアヂアゾルBTの蛍光分子青色発光：　発光分子基はフルオレンPFの蛍光分子

パワー効率１.9cd/A、最高輝度3585cd/m2

J.X. Jiang et al, Adv. Mater. 18(2006)1769.

PF BT

Phq

Phosphorescence

White light using color conversion method

Green (515 nm) phosphorescence emitter : Ir(ppy)3

ITO/α-NPD/6.2mol% Ir(ppy)3:TCTA/CF-X/Alq

3/LiF/Al

TCTA host; ηext= 19.2 % M. Ikai et al., APL 79 (2001)156.

Blue (465nm) phosphorescence emitter: Firpic

ITO/CuPc/α-NPD/6%FIrpic:host/BAlq/LiF/Al

CBP host; ηext= 6.1%, 7.7 lm/W

mCP host; ηext= 7.5%, 8.9 lm/W R.J. Holmes et al., APL 82(2003)2422.

Cathode Anode

Electron Hole

Conduction Band(LUMO)

Valence Band(HOMO)

Electron-Hole Capture; Exciton

Singlet Exciton Triplet Exciton

Light Emission Heat Dissipation

Light Output Internal Decay

ηηηηout

Scheme of EL Process

γγγγ

ηηηηex

ηηηηr

External quantum efficiencyηηηηext (%) = γ ηγ ηγ ηγ ηex ηηηηr ηηηηout

= ηηηηint ηηηηout

γ : γ : γ : γ : carrier injection balance

ηηηηex : exciton formation efficiency

ηηηηr : exciton recombination efficiency

0.25 for singlet exciton, 1.0 for triplet exciton

ηηηηout : outcoupling effi. for light from OLED

ηηηηout ~ 1/2na2 (=20%)

Phosphorescent emitters

ηηηηint =100% , ηηηηext (%) = 20 %

Host materials for blue emitters

400 440 480 520 560 6000

1

2

3

4

0.00

0.05

0.10

0.15

0.20

0.25

PL in

tensity (

arb

. un

its)

PL

in

ten

sity (

arb

. un

its)

wavelength (nm)

CBP on quartz

x15

T1 emission

12 KS

1 emission

375 400 425 450 475 500 525 550 5750

2

4

6

8

em

issio

n inte

nsity (

arb

. units)

wavelength (nm)

1 FIrpic/CBP

2 FIrN4/CBP

3 FIrpic/SimCP

4 FIrN4/SimCP

CBP

CBP

1

1

2

2

3

4

λexc

=300nm at 10K

T1emission

S1 emission

ITO/CuPc/α-NPD/6%FIrpic:host/BAlq/LiF/Al

CBP: 6.1%, 7.7 lm/W

mCP:7.5%, 8.9 lm/W R.J. Holmes et al., APL 82(2003)2422.

Currently very weak efficiency

Highly stable (high glass transition temp.),

high carrier mobility,

high T1 energy level hosts are necessary.

The best host material for blue emitter in OLEDS

mCP SimCP SimCP2SimCP2SimCP2SimCP2

Si

N

N

N

N

5.0 5 .2 5 .4 5 .6 5 .8 6 .0 6 .2 6 .4

0

500

1000

1500

2000

Co

un

tin

g R

ate

(c

ps

)

Energy(eV)

non-annea led

70oC

120oC

150oC

100 200 300 400 500 600 700 800

10-4

10-3 : (e) Electron carrier mobility

Carr

ier

mob

ility

(cm

2/V

s)

Electric field1/2

(V/cm)1/2

SimCP2

(h)

(e)

mCP

(h)(e)

(h)

(e)

SimCP

: (h) Hole carrier mobility

280 320 360 400 4400.0

0.2

0.4

0.6

0.8

1.0

1.2PLE

PL

in

ten

sity (

no

rma

lize

d)

wavelength (nm)

1 3wt% PL

2 15wt% PL

3 20wt% PL

4 3wt% PLE

5 20wt% PLE

1

24

3

10K

5PL

T. Tsuboi., M.-F. Wu, S.-W. Liu, C.-T. Chen, Org. Electron. (2009), in press.

SimCP2: Tg= 148 CmCP: 55 C

SimCP: 101 C

CBP: 62 C

ηext of 17.7 % and power efficiency of 24.2 lm/W at 100 cd/m2 for FIrpic

ITO/PEDOT:PSS(35nm)/14 wt% FIrpic:SimCP2(35nm)/TPBi(28nm)/LiF/Al

c.f., 10.4 and 5.9 lm/W in the case of SimCP and mCP hosts, respectively

SimCP2 HOMO : 6.12 eV

LUMO : 2.56 eV,

bis(3,5-di(9H-carbazol-9-yl) phenyl)diphenylsilane (SimCP2)

Copolymer with Rare-earth-complex organic molecules

Eu

high color purity with sharp lines

Tb

Tb

Eu

White OLED with rare-earth small molecules

(a) (b)

Z. Kin et al., Mater. Res. Soc. Symp. Proc. Vol. 965(2007) 0965-S04-02

Eu

Sm

PBDFIrpic

Small molecule: Dual emission from a single molecule

J.H. Seo et al, Thin Solid Films 516(2008)3614.

Max: 11.0 cd/m2, 5.60 lm/W

Ir(dfppy)2(acac): 469nm PL

Ir(pq)2(acac): 597nm PL

Host: UGH2

1,4-phenylenesis (triphenylsilane)

473nm: Ir(dfppy) 544nm: Ir(pq)