Light Extraction in OLED with Corrugated Substrates Franky So Department of Materials Science and Engineering North Carolina State University Raleigh, NC 27695-7907 1
Where Did the Light Go? Modes Distribution in OLED Optical Modes and In-plane Wave-vector Light Extraction Techniques 2
Optical Modes in OLED Internal quantum efficiency (η int ) : ~ 100% External quantum efficiency (η ext ) : ~25% ITO/organic waveguide mode : ~50% Substrate mode : ~25% Extracted mode : ~20-25% ext out int χ out : ~20-25% Al Organic ITO TM0 (SP) TE0 ITO/organic mode Glass Substrate mode Escape cone Air mode
Optical Modes ETL Thickness Dependence Appl. Phys. Lett. 97, 253305 (2010) 4
In-plane Wave-vector k x =0 Air 2.8 Simulated Mode Distribution k 0 n glass k 0 z Glass x ITO Organic Metal k x = k 0 Sub WG SPP Photon Energy (ev) 1.9 Air Sub 0 k x (μm-1) 25 Wave-vector k In the air k 0 = 2π/λ In an organic layer k = n org k 0 k = k x 2 + k z 2 5
Optical Modes in Green OLED Simulation Structure Simulated Mode Distribution Cs 2 CO 3 /Al Alq3: Cs 2 CO 3 (30nm) B3PYMPM (10nm) CBP:Ir(ppy) 2 (acac) (20nm, 7%) TAPC (40nm) MoO x (10nm) ITO(100nm) λ=520nm Air (30%) Sub(24%) EL Spectrum of Ir(ppy) 2 (acac) k x (μm -1 ) λ=520nm Photons couple into each optical mode Only 30% can emit into air 16% is trapped in waveguided mode 26% is trapped in SPP mode 6
Light Extraction Techniques Light extraction techniques to improve OLED light outcoupling Extracts substrate, waveguided and SPP modes Sub-anode grids Corrugation Half-ball lens Microlens arrays Porous substrate 7
Extracting Light with Corrugation OLED on PDMS/Al Corrugation OLED on Corrugated Glass Substrate OLED on Corrugated Sapphire Substrate 8
Corrugated OLED on PDMS/Al I-V-L LiF & Al cathode 70 nm Bphen 15 nm CBP:Irppy3 15 nm TCTA:Irppy3 50 nm TAPC 100 nm ITO 15 nm Al Current density (ma/cm 2 ) 10 1 0.1 0.01 1E-3 1E-4 1E-5 Buckling Reference 10 5 10 4 10 3 10 2 10 1 10 0 Luminance (cd/m 2 ) 1E-6 0 1 2 3 4 5 6 7 8 Voltage (V) 10-1 9
Corrugated OLED on PDMS/Al Efficiency Current efficiency (cd/a) 100 80 60 40 20 100 80 60 40 20 Power efficiency (lm/w) Efficiency at 1000 cd/m 2 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 0 0 10 100 1000 10000 Luminance (cd/m 2 ) Adv. Opt. Mater. 1, 404 (2013) 10
Angular Dependence EL spectrum Angular dependence EL intensity 0 20 40 60 Buckling Ref. 0 2.0 1.5 1.0 0.5 30 60 Reference Buckling Lambertian 500 550 600 650 Wavelength (nm) 0 Emission angle ( ) 90 EL spectrum Enhancements over all λ & angles Angular dependence Lambertian distribution Adv. Opt. Mater. 1, 404 (2013) 11
OLED on Corrugated Glass Substrate High efficiency planar control device Combined light extraction methods Corrugated epoxy glass extracts waveguided mode and SPP mode Macrolens extracts substrate mode Planar Al Corrugated with lens Al Organic Layers Organic Layers ITO Glass ITO Glass Hemisphere Lens 12
OLED on Corrugated Glass Substrate LiF/Aluminum NBphen (20nm) 3TPYMB (20nm) CBP:Ir(ppy) 2 (acac) (30nm, 7%) TAPC (40nm) MoO x (10nm) ITO Corrugated Epoxy Glass Substrate Hemi Sphere Lens 13 13
OLED on Corrugated Glass Substrate Corrugated Device with Lens Corrugated Device Planar Device 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. 14
OLEDs on Mode High distribution Index Substrates Normal glass substrate n = 1.5 High index glass n = 1.8 Surface Plasmon Waveguide Surface Plasmon Absorption Absorption Substrate Substrate Air Air Air mode Substrate mode Absorption loss Waveguide mode 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%
Corrugated High Index Substrate Silica sphere diameter: 500 nm 10 sccm of BCl 3, 25 sccm of Cl 2 and 10 sccm of Ar
Corrugated Sapphire Substrate SEM images Nominal periodicity: 500 nm Corrugation depth: 90 nm
OLED on Corrugated Sapphire Substrate Plain Grating Al/LiF 3TPYMB TCTA :Irppy 3 CBP :Irppy 3 TAPC ITO HI glass Index matching gel Sapphire macro lens
Extraction of Substrate Mode by Macrolens EQE Current efficiency 100 250 EQE (%) 80 60 40 20 Plain 260nm grating Current efficiency (cd/a) 200 150 100 50 Plain 260nm grating 0 10 100 1000 10000 Luminance (cd/m 2 ) 0 10 100 1000 10000 Luminance (cd/m 2 ) Peak comparison 63 %EQE and 225 cd/a for grating devices (20 ~25% up) 52 %EQE and 178 cd/a for plain devices ACS Appl. Mater Interface 7, 8974 (2015) 19
Extraction of Substrate Mode by Macrolens OLED Glass or high index glass Normalized Intensity (a.u.) Normalized Intensity (a.u.) 3 2 1 0 3 2 1 0 Plain glass without macrolens with lacrolens Plain high index glass 450 500 550 600 650 700 450 500 550 600 650 700 Wavelength (nm) 500nm grating glass 500nm grating high index glass Wavelength (nm) Current efficiency (cd/a) Plain glass Plain high index glass 500nm grating glass 500nm grating high index glass 168 178 184 225
Extraction of Substrate Mode by Macrolens Macrolens OLED High index glass Current Efficiency (cd/a) Planar normal glass Planar high index glass Grating high index glass 168 173 210 EQE (%) 46 52 63 Extraction of waveguided mode Extraction of SPP mode