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Light Extraction in OLED with Corrugated Substrates
Franky So
Department of Materials Science and EngineeringNorth Carolina State University
Raleigh, NC 27695-7907
1
Where Did the Light Go?
2
• Modes Distribution in OLED
• Optical Modes and In-plane Wave-vector
• Light Extraction Techniques
Glass
Organic
Al
ITO
TM0 (SP)
TE0
� Internal quantum efficiency (ηint) : ~ 100%
� External quantum efficiency (ηext) : ~25%• ITO/organic waveguide mode : ~50%
• Substrate mode : ~25%
• Extracted mode : ~20-25%
ITO/organic mode
Substrate mode
Air mode
Escape cone
intoutext KFK
χout : ~20-25%
Optical Modes in OLED
Optical Modes – ETL Thickness Dependence
4
Appl. Phys. Lett. 97, 253305 (2010)
In-plane Wave-vector
Wave-vector k• In the air k0 = 2π/λ• In an organic layer k = norgk0• k = kx
2 + kz2
z
x Metal
Organic
ITO
Glass Sub
kx=0
kx= k0
Air
WG
SPP
Simulated Mode Distribution
SubAir
kx(μm-1)P
hoto
n E
nerg
y (e
V)
k0 nglassk0
5
0 251.9
2.8
Optical Modes in Green OLEDSimulated Mode Distribution
• Photons couple into each optical mode • Only 30% can emit into air• 16% is trapped in waveguided mode• 26% is trapped in SPP mode
λ=520nm
Air (30%) Sub(24%)
kx (μm-1)
λ=520nm
EL Spectrum of Ir(ppy)2(acac)
MoOx (10nm)
TAPC (40nm)
CBP:Ir(ppy)2(acac)(20nm, 7%)
B3PYMPM (10nm)
Alq3: Cs2CO3 (30nm)
Cs2CO3/Al
ITO(100nm)
Simulation Structure
6
Light Extraction Techniques
• Light extraction techniques to improve OLED light outcoupling • Extracts substrate, waveguided and SPP modes
Sub-anode grids Corrugation Microlens arrays Porous substrateHalf-ball lens
7
Extracting Light with Corrugation
8
• OLED on PDMS/Al Corrugation
• OLED on Corrugated Glass Substrate
• OLED on Corrugated Sapphire Substrate
15 nm Al100 nm ITO
LiF & Al cathode
50 nm TAPC
70 nm Bphen15 nm CBP:Irppy315 nm TCTA:Irppy3
0 1 2 3 4 5 6 7 81E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10 Buckling Reference
Lum
inan
ce (c
d/m
2 )
Cur
rent
den
sity
(mA/
cm2 )
Voltage (V)
10-1
100
101
102
103
104
105
I-V-L
Corrugated OLED on PDMS/Al
9
¡ Efficiency at 1000 cd/m2
• Ref. : 50.8 cd/A, 30.3 lm/W
• Buckling : 79.2 cd/A, 56.7 lm/W
¨ 56% enhancement in cd/A and
87% enhancement in lm/W
10 100 1000 100000
20
40
60
80
100
Pow
er e
ffici
ency
(lm
/W)
Cur
rent
effi
cien
cy (c
d/A)
Luminance (cd/m2)
0
20
40
60
80
100
Efficiency
Adv. Opt. Mater. 1, 404 (2013)
Corrugated OLED on PDMS/Al
10
0
30
60
90
Reference Buckling Lambertian
Emission angle (q)0
0.5
1.0
1.5
2.0
500 550 600 650
0q 20q 40q 60q
Buckling Ref.
EL in
tens
ity
Wavelength (nm)
EL spectrum Angular dependence
¡ EL spectrum
• Enhancements over all λ & angles
¡ Angular dependence
• Lambertian distribution
Adv. Opt. Mater. 1, 404 (2013)
Angular Dependence
11
– High efficiency planar control device– Combined light extraction methods
• Corrugated epoxy glass extracts waveguided mode and SPP mode• Macrolens extracts substrate mode
Organic Layers
ITO
Al
Glass
Organic Layers
ITO
Glass
Al
Hemisphere Lens
Planar Corrugated with lens
OLED on Corrugated Glass Substrate
12
OLED on Corrugated Glass Substrate
13
Hemi Sphere Lens
Glass SubstrateCorrugated Epoxy
ITO MoOx (10nm) TAPC (40nm)
CBP:Ir(ppy)2(acac)(30nm, 7%)
3TPYMB (20nm)NBphen (20nm)LiF/Aluminum
13
• Over 60% EQE achieved on corrugated 3TYPMB device • Over 25% enhancement by corrugation • 2.7 times enhancement by combining corrugated substrate and hemi
sphere lens.
Corrugated Device with Lens
Corrugated Device
Planar Device
OLED on Corrugated Glass Substrate
14
Surface Plasmon
Waveguide
Absorption
Substrate
Air
Mode distribution
Air mode Substrate mode Absorption loss Waveguidemode SP mode
Normal glass 20~25% 20~25% 5~10% 20~25% 30~35%
High index glass 20~25% 30~35% 5~10% 0 35~40%
Normal glass substrate n = 1.5 High index glass n = 1.8
Surface Plasmon
Absorption
Substrate
Air
OLEDs on High Index Substrates
10 sccm of BCl3, 25 sccm of Cl2 and 10 sccm of Ar
Silica sphere diameter: 500 nm
Corrugated High Index Substrate
SEM images
Corrugation depth: 90 nm
Nominal periodicity: 500 nm
Corrugated Sapphire Substrate
HI glass
ITO
TAPCCBP :Irppy3
TCTA :Irppy3
3TPYMBAl/LiF
Plain Grating
Index matching
gel
Sapphire macro lens
OLED on Corrugated Sapphire Substrate
Extraction of Substrate Mode by Macrolens
19
EQE Current efficiency
¡ Peak comparison
• 63 %EQE and 225 cd/A for grating devices (20 ~25% up)
• 52 %EQE and 178 cd/A for plain devices
10 100 1000 100000
20
40
60
80
100
Plain 260nm grating
EQE
(%)
Luminance (cd/m2)
10 100 1000 100000
50
100
150
200
250
Cur
rent
effi
cien
cy (c
d/A)
Luminance (cd/m2)
Plain 260nm grating
ACS Appl. Mater Interface 7, 8974 (2015)
0
1
2
3
Norm
alize
d In
tens
ity (a
.u.)
Plain glass without macrolens with lacrolens
450 500 550 600 650 7000
1
2
3
Wavelength (nm)
Norm
alize
d In
tens
ity (a
.u.)
Plain high index glass
500nm grating glass
450 500 550 600 650 700
Wavelength (nm)
500nm grating high index glass
Plain glass Plain high index glass
500nm grating glass
500nm grating high index glass
Current efficiency (cd/A) 168 178 184 225
OLEDGlass or high index glass
Extraction of Substrate Mode by Macrolens
OLEDHigh index glass
Macrolens
Planar normalglass
Planar high index glass
Grating high index glass
Current Efficiency (cd/A) 168 173 210
EQE (%) 46 52 63
Extraction of waveguided mode
Extraction ofSPP mode
Extraction of Substrate Mode by Macrolens
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