White Organic Light Emitting Diodes for Super-thin Flat ...skaczmarek.zut.edu.pl/To Poland LAquila...
Transcript of White Organic Light Emitting Diodes for Super-thin Flat ...skaczmarek.zut.edu.pl/To Poland LAquila...
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)