Hi h ffi i hit OLED f di lHigh efficiency white OLED for display and lighting applicationsand lighting applications
2009.09.18
Jun Yeob Lee
Organic Electronics Laboratory, Dankook University, Korea
White light-emitting diodes
G l li h iLi h
Application of white OLEDs
General lightingLight sourceni
t)In
tens
ity (a
rb. u
GE Philips400 500 600 700 800
Wavelength (nm)
Device structure of white OLEDsSingle layer white OLEDsSimple device structure
Stacked white OLEDsGood device performances
Device structure of white OLEDs
Poor device performancesSuitable for polymers
pGood color stabilitySuitable for small molecules
RGB or YB
Materials for white OLED
Fluorescent OLED Phosphorescent OLED
Emission process
Singlet to singlettransition
Triplet to singlet transition
Efficiency 25 %(internal efficiency) 100 %(internal efficiency)25% 75% 100%
Emitter Organic or organometallic Organometallic(Ir, Pt, Os,…complex)
N
Emission Singlet Triplet
NIr
N
Emission mode
Singlet Triplet
High efficiency phosphorescent white OLEDs
All phosphorescent white OLEDs
Quantum efficiency : > 15 %, Q y ,Lifetime : >200,000 h@1,000 cd/m2
CIE : (0.47,0.45)
UDC, SID 2008
High efficiency phosphorescent white OLEDs
Hybrid white OLEDs
Singlet blue/red and green tripletQuantum efficiency : 18.4%
Forrest et al. Nature. 440, 908(2006)
High efficiency phophorescent white OLEDs
Tandem OLED(Multiphotoemission)
Emission Layer Hole Transport Layer
Electron Transport LayerCathode
Cathode
Emissive unit Glass substrate
AnodeHole Injection Layer Hole Transport Layer
Charge generation layer
Emissive unitEmissive unit
Charge generation layer
Emissive unitAnode
ITO, WO3, V2O5, NPD:F4-TCNQ
BCP:Li, BCP:Cs
White lightForrest et al. Adv. Mater. 18, 339(2006)
Comparison of white OLEDs
All phosphorescent
hybrid tandem
Quantum efficiency 15 ~ 20 % 15 ~ 20 % 20 ~ 35 %
Driving voltage 5 ~ 6 V 5 ~ 6 V ~ 8-9 V
Color purity bad good goodp y g g
Lifetime >100, 000 h >100, 000 h >> 100,000 h
Bl lif i Bl lif iProblem
Blue lifetimeColor stability
Efficiency roll-off
Blue lifetimeColor stability
Efficiency roll-off
Complicated process
Efficiency roll-offEfficiency roll off Efficiency roll off Efficiency roll off
Comparison of OLED as a display and lighting
Display lightingDisplay
휘도 : 100 ~ 500 cd/m2
수명 : >10 000 30 000 h
lighting
휘도 : >1000 cd/m2
수명수명 : >10,000 ~ 30,000 h높은 색순도
고정세넓은 색재현 범위
수명 : >10,000 h높은 연색지수대면적 구현
넓은 색재현 범위낮은 소비전력
TFT 구동
낮은 소비전력저가 공정 구현
Key performances of white OLEDs
High quantum efficiencyHigh quantum efficiency
Low driving voltage : P-I-NHigh mobility common layer
C l t bilit b l d bi ti hiftColor stability : balanced recombination zone shift
Little efficiency roll-off : little charge leakageLittle efficiency roll off : little charge leakagebroad recombination zone
High color rendering index for lighting
P re RGB emission for displaPure RGB emission for display
High quantum efficiency in sky blue and white OLED for lightingwhite OLED for lighting- New blue phosphorescent host material
- New orange phosphorescent host material
Advantages of spiro structure
•High thermal stability
•Morphological stability•Morphological stability
•Good Electron transporting properties
•Photochemical stability•Photochemical stability
•Blue emission
•Chemical versatility•Chemical versatility
•Wide triplet bandgap(2.9 eV)
Synthesis of SPPO1
PCl
MC SPPO 1341 nmP
PO
Br
MC
H2O2
0.15
0.20
UV
SPPO 1BG = 324 nm, 3.82eVET = 444 nm, 2.79 eV
Ia.u.
) 0.8
1.0444 nm308, 316 nm341 nm
PL at 77K PL at 298K
2-diphenylphosphine oxide-9,9′-spirobifluorene (SPPO1)
0.05
0.10
ntensity(a.u.)Abs
orba
nce(
a
0.4
0.6
300 400 500 6000.00
0.05 )A
Wavelength(nm)
0.0
0.2
Wavelength(nm)
J. Y. Lee et al. submitted (2008)
Device performances of SPPO1
25 mCP
LiF/Al (200 nm) Quantum efficiency : 17 %
15
20SPPO1 PEDOT/SPPO1 PEDOT/TCTA/SPPO1
Effic
ienc
y (%
)Alq3 (20 nm)
SPPO1:FIrpic (30 nm,10%)BCP (5 nm)
mCP (5 nm)
(0.15,0.33)
0
5
10
Qua
ntum
E
NPB (20 nm)
ITO
DNTPD (60 nm)
ITO
DNTPD (60 nm)
40
8000
0 1 10 100 1000 100000
Luminance (cd/m2)
ITOITOGlass
30
40
ty(m
A/c
m2 )
mCP SPPO1 PEDOT/SPPO1 PEDOT/TCTA/SPPO1 6000
8000 mCP SPPO1 PEDOT/SPPO1 PEDOT/TCTA/SPPO1
e (c
d/m
2 )
10
20
Cur
rent
Den
sit
2000
4000
Lum
inan
ce0 2 4 6 8 10
0
Voltage(V)0 2 4 6 8 10
0
Voltage (V)
SPPO1 in simple device structure
Q. E. : 19.4 %(0 15 0 33)(0.15,0.33)
J. Y. Lee et al. Appl. Phys. Lett. 94, 013301(2009)
SPPO1 as a host in WOLEDs
SPPO1
LiF/Al 120
cm2 ) 15000
Device I(current density) 20
%) 50
A)
mCP
SPPO1:Firpic:Ir(pq)2acac
SPPO1
TCTA 60
90
ensit
y (m
A/c
6000
9000
12000
ance
(cd/
m2 )Device II(current density)Device I (luminance)Device II(luminance)
8
12
16
m e
ffici
ency
(%
20
30
40
effic
ienc
y (c
d/A
Device I(quantum eff )
ITO
PEDOT:PSS
NPB
0
30
Cur
rent
de
0
3000
6000
Lum
ina
0
4
8
1 10 100 1000 10000
Qua
ntum
0
10
20
Cur
rent
eDevice I(quantum eff.)Device II(quantum eff.)Device I(current eff.)Device II(current eff.)
D i I d 0 7 %
2.4 2 72.42.4
0 2 4 6 8
Voltage (V)
1 10 100 1000 10000
Luminance (cd/m2)Device I : red 0.7 %Device II : red 1.0 %
NPD
2.4 2.7
2.8
PEDOT
3.1
BCP
2.42.8
Alq3
3.0
FIrpic
TCTA
2.4
Ir(pq)2acac
3.0
(arb
. uni
t) Device I
Device II
5.5 5.6mCP
5.1
BCP
6.1 SPPO1 6.1
Alq3
5.85.7
5.2
Inte
nsity
6.5 400 500 600 700 800
Wavelength (nm)
J. Y. Lee et al. Optics Letters. 34, 407(2009)
Stacked WOLEDs
J. Y. Lee et al. submitted(2009)
Stacked WOLEDs
(0.37,0.43) 27.5 cd/A
New SPPO2 material
Roughness : 0.3 nm Triplet energy : 2.4 eVJ. Y. Lee et al. J. Mat. Chem. In press(2009)
SPPO2 as an electron transport material
Electron only device high electron density in the SPPO2
SPPO2 as the electron transport layer in green
SPPO2 as an electron transport material in blue
Phosphorescent orange host material
J. Y. Lee et al. Org. Electron. 10, 998(2009)
Deep blue and pure white phosphorescent OLED for displayOLED for display
deep blue phosphorescent device- deep blue phosphorescent device
- pure white phosphorescent devicep p p
Deep blue phosphorescent materials
(0.13,0.14)
BASF SID 2006
Deep blue phosphorescent materials
Chi et al. Adv. Mater. ASAP 2009 Wu et al. Angew. Chem. Int. Ed. 47, 4542 2008
Blue phosphorescent dopant materials
NIr
FN
Ir
NIr
FN
I
F
3
NC
FIr
FNC
F
F
3
Ir
3333
475 nm 464 nm 452 nm523 nm
Blue shift by electron withdrawing substituent in phenylBlue shift by electron donating substituent in pyridine
Deep blue phosphorescent dopant materials
(0.15, 0.16), 11 cd/A
J. Y. Lee et al. Org. Electron. 10, 170(2009)
Pure white OLEDs using deep blue material
LiF/Al
Alq3
LiF/Al
Alq3
LiF/Al
Alq3
LiF/Al
Alq3
mCP:FCNIr(20 nm)
BCP
q3
TCTA:TAZ:Ir(ppy)3:Ir(pq)2acac
mCP:FCNIr(15 nm)
BCP
q3
TCTA:TAZ:Ir(ppy)3:Ir(pq)2acac
mCP:FCNIr(10 nm)
BCP
q3
TCTA:TAZ:Ir(ppy)3:Ir(pq)2acac
mCP:FCNIr(15 nm)
BCP
q3
TCTA:TAZ:Ir(ppy)3:Ir(pq)2acac30 nm
TCTA
ITO
PEDOT:PSS
NPB
mCP
ITO
PEDOT:PSS
NPB
mCP
ITO
PEDOT:PSS
NPB
mCP
ITO
PEDOT:PSS
NPB
mCP
100D i I
10000
ITO ITO ITO ITO
Device I Device II Device III Device IV
60
80
nsity
(mA
/cm2 ) Device I
Device IIDevice IIIDevice IV 6000
8000
nce
(cd/
m2 )
Device I
Device II
Device III
Device IV
20
40
Cur
rent
den
2000
4000
Lum
inan
00 2 4 6 8 10
Voltage (V)
00 2 4 6 8 10
Voltage (V)
J. Y. Lee et al. Org. Electron. 10, 681(2009)
Pure white OLEDs using deep blue material
CIE Current ffi iefficiency
Device I (0.28,0.31) 21 cd/A
Device II (0.30,0.31) 21 cd/A
30
Device III (0.35,0.34) 25 cd/A
Device IV (0.30,0.31) 28 cd/A
20
25
30
cy (c
d/A
)
uni
t) Device IDevice IIDevice III
10
15
ent e
ffici
enc
Device IDevice II en
sity
(arb
. Device IIIDevice IV
0
5
0 2000 4000 6000 8000 10000
Cur
re Device IIIDevice IV
400 500 600 700 800
Inte
0 2000 4000 6000 8000 10000Luminace (cd/m2)
400 500 600 700 800
Wavelength (nm)
EL spectra according to luminance
t) (0.30,0.33)
(arb
. uni
t (0.30,0.33)
7500 cd/m2
(0.30,0.31)
630 cd/m2
Inte
nsity
630 cd/m
400 500 600 700 800
I
(0.29,0.31)
270 cd/m2
400 500 600 700 800
Wavelength (nm)
New fabrication method of WOLEDNew fabrication method of WOLED
- stamp transfer printingstamp transfer printing
Stacked polymer white light-emitting diodes
Stacked double layer emitting structure in polymer white LEDs
toluene soluble
alcohol soluble
Xie et al. Appl. Phys. Lett. 90, 203513, 2007
Printing method to form orthogonal polymer filmsPrinting method to form orthogonal polymer filmsTransfer printing Laser induced thermal imaging
Bradley et al. Adv. Mater. 20, 1679, 2008 Lee et al. Adv. Mater. 16, 51, 2004
Stamp transfer printing process
SiITO
Yellow polymerPEDOT:PSS
PDMS
metal cathode
J. Y. Leet et al. Org. Electron. 10, 372(2009)
AFM of Yellow Polymer Films
S i ti St t f i tiSpin coatingSurface roughness : 0.5 nm
Stamp transfer printingSurface roughness : 0.4 nm
Comparison of hole only devices
Hole current density increase by stamp transfer printing
ITO/PEDOT:PSS/SY/Al
35004000
A/c
m2 )
spin coatingT f i ti
2000
25003000
nsity
(mA Transfer printing
Yellow polymer
Al
++ + + + +
++ + + + +
500
10001500
urre
nt d
en
ITO
PEDOT:PSS
0500
0 1 2 3 4 5
V lt (V)
Cu
Voltage (V)
Comparison of device performances
Current density and luminance increase by stamp transfer printingC t ffi i i b t t f i tiCurrent efficiency increase by stamp transfer printing
ITO/PEDOT:PSS/SY/LiF/Al
2000
)
30000 4
1500
y (m
A/c
m2 )
20000
25000
ce (c
d/m2 )Spin coating
Transfer printing3
ency
(cd/
A)
500
1000
rent
den
sity
10000
15000
Lum
inan
c1
2
rren
t effi
cie
Spin coating
00 1 2 3 4 5
Cur
0
5000
00 5000 10000 15000 20000 25000 30000
Cur Transfer printing
Voltage (V) Luminace (cd/m2)
Comparison of emission spectrum
Same spectrum irrespective of film coating method
. uni
t) Spin coating
Transfer printing
nsity
(arb
.In
ten
400 500 600 700 800
Wavelength (nm)
Comparison of lifetime
Lifetime was doubled by stamp transfer printing process
Current density : 40 mA/cm2
80
100
) 4
4.5spin coatingTransfer printing
60
nanc
e (%
3.5
4
tage
(V)
20
40
Lum
in
3
Vol
t
00 50 100 150 200
2.5
Time (h)
Stamp transfer printing of soluble small molecules
J. Y. Leet et al. Org. Electron. 10, 978(2009)
Stamp transfer printing process for white deviceSi
ITOSi
ITO
Yellow polymerPEDOT:PSS
Yellow polymerPEDOT:PSS
PDMS Blue polymerPDMS Blue polymer
l h dl h dmetal cathodemetal cathode
J. Y. Leet et al. J. Phys. D. 42, 105115(2009)
Multilayer white polymer light-emitting device
2.4
2.5Low current density in the white device due to poor 2.9
PEDOTBl
YellowLiF/Al
hole injection into blue emitting layer
5.1
4.85.0
Blue
ITO
5.4
1000
cm2 ) B(30 nm)/Y(30 nm)
B(20 nm)/Y(20 nm) 80009000
10000
m2 )
B(30 nm)/Y(30 nm)B(20 nm)/Y(20 nm)B(30 nm)
600
800
nsity
(mA
/c B(30 nm)Y(30 nm)
40005000600070008000
nanc
e (c
d/m2 B(30 nm)
Y(30 nm)
200
400
Cur
rent
den
01000200030004000
Lum
in
00 1 2 3 4 5 6 7 8
Voltage (V)
00 1 2 3 4 5 6 7 8
Voltage (V)
Efficiency of WPLEDs
High efficiency compared with corresponding single layer devices
5
4
5y
(cd/
A) B(30 nm)/Y(30 nm)
B(20 nm)/Y(20 nm)B(30 nm)Y(30 nm)
2
3
t effi
cien
cy
0
1
Cur
rent
00.1 1 10 100 1000 10000
Luminace (cd/m2)
Electroluminescence spectra of WPLEDs
Balanced red and green emission in multilayer WPLEDs
Color coordinate (0.34, 0.41)
unit)
B(30nm)/Y(30nm)B(20nm)/Y(20nm)B(30 nm)
ity (a
rb. u Y(20 nm)
Inte
nsi
400 500 600 700 800
W l th ( )Wavelength (nm)
WPLEDs with QD interlayer
QD interlayer forcolor control in WPLEDs
J. Y. Leet et al. Appl. Phys. Lett. 94, 093303(2009)
AcknowledgementS. O. Jeon (Ph.D, 4학기)- OLED material synthesis- Organic memory
S. U. Jang (MS, 2학기)- OLED material synthesis
g y- Organic solar cell
K S Yook (Ph D 1학기) H. S. Son (MS, 2학기)K. S. Yook (Ph.D, 1학기)- White OLED- Organic bistable LED
H. S. Son (MS, 2학기)- OLED material synthesis- Solar cell material synthesis
C. W. Joo (MS, 4학기)- Polymer WOLED Undergraduate
Y. J. Cho C. W. Suh