Enhancement of Light Extraction Efficiency in Organic Light Emitting Device with Multi-Stacked Cathode and High Refractive Index Anode

Transcription

1 Enhancement of Light Extraction Efficiency in Organic Light Emitting Device with Multi-Stacked Cathode and High Refractive Index Anode Kanazawa Institute of Technology, Jaan Akiyoshi Mikami and Takao Goto Background and objective Theoretical analysis of otical mode & out-couling efficiency Suression of surface-lasmon loss by multi-cathode structure Device erformance of PH-OLED with high refractive index medium

2 Power Density in OLED calculated by FDTD Simulation Random Diole Glass Glass mode OLED OLED (~200nm) n=1.6~1.9 Waveguide mode Surface Plasmon Emission oint 5 μm Glass ITO NPB Alq 3 Al ~200 nm

3 Power Density from μ, μ // Diole Emission in OLED Random Diole Glass mode OLED Waveguide mode Surface Plasmon Horizontal Diole Vertical Diole ITO NPB Alq 3 Al 2 μm 5 μm

4 Power Density from μ, μ // Diole Emission in OLED Electro-Magnetic Interaction of Point Diole in Organic LED Anode Proagation Wave mode 0~200nm Organic Layers Waveguide mode Surface Plasmon-olariton Metal (Al, Ag) Cathode Evanescent Wave Lossy Surface Wave Otical Power Horizontal Diole Vertical Diole ITO NPB Alq 3 Al 2 μm 5 μm

5 Power Density from μ, μ // Diole Emission in OLED Otical Mode (Ray otics) mode (Wave otics) Waveguide mode (Electro-magnetic) Surface Plasmon (Near-field otics) Lossy Surface Wave Electro-Magnetic Interaction of Point Diole in Organic LED k k Sub k WG k SP k LSW z k Z k Z k 1 Multi-scale Otical Analysis Horizontal Diole k h k 2 1 k y 2 h x Otical Power Vertical Diole mode Waveguide mode Surface Plasmon-olariton Lossy Surface Wave 2 μm ITO NPB Alq 3 Al 5 μm

6 Micro-Scale Near-field otics #Electro-magnetic calculation in oint diole Electro-magnetic otics #FDTD Flow-chart of Multi-scale Otical Analysis ΤE Horizontal P // k // Diole moment Vertical ΤΜ Radiation of Dioles Angular sectrum of Polarization (s,) P TM k // Power dissiation in k-sace s 2 θ 2 x y y μ v z s θ φ 2 2 θ 2TM sin θ cos θ x y μ h k 1 I xy x Wave otics # Fresnel s theory # Transfer matrix # RCWA Ray otics # Ray tracing Macro-Scale Multile Internal Reflection in Thin films Incoherent Otics in Luminescent Characteristics Out-couling Analysis d z Luminance & Efficiency Emission Sectrum Otical Mode Intensity Angular deendence Angular Behavior of s & olarized emission

7 Power Sectrum of Diole Emission in Green OLED Otical Power Density λ:520nm Horizontal Diole z PEDOT (40nm) CBP:ir(y) 3 (20nm) Bu-PBD(0-300nm) LiF 3 (~1nm) Al (0nm) μ h D dm μ ν Vertical Diole Waveguide TM (c) D dm =250nm External SP k Z k 1 k // y x ITO 0nm PE-DOT :PSS 40nm -5.1 N N Ir N Ir(y) 3 Ir(y)3-2.4 NPB 20nm CBP: Ir(y) 3 20nm N CBP -2.7 ETL 50nm -6.4 N Energy Potential Diagram LiF/Al 0.5/0nm -4.3 (b) D dm =150nm (a) D dm =50nm TM TM SP In-lane Wave Vector (k h ) SP Waveguide SP LSW

8 Otical Power Density Otical Power Density Otical Power Density PEDOT (40nm) CBP:ir(y) 3 (20nm) Bu-PBD(0-300nm) LiF 3 (~1nm) Al (0nm) 0% 80% Dissiated Power Density of Each Otical Mode in PH-Green OLED λ:520nm μ h D dm μ ν (b) Horizontal diole 9% Waveguide mode Otical Mode Lossy Surface Wave Surface Plasmon (Metal Cathode) Waveguide mode (Thin films) mode (Thick films) (Out-couling) 12% Surface Plasmon & LSW k LSW k SP k WG k Sub k 0% 80% 60% 40% 20% 0% 0% 80% (a) Random diole 47% Surface Plasmon loss Lossy Surface Wave 8% Waveguide mode 22% mode 23% Distance between Diole and Cathode [nm] (c) Vertical diole 88% Surface Plasmon loss Lossy Surface Wave 60% 36% mode 60% 6% Waveguide mode 40% 40% 20% 42% 20% 6% mode 0% Distance between Diole and Cathode [nm] 0% Distance between Diole and Cathode [nm]

9 Luminance [cd/m 2 ] Device Performance of Normal Tye Green PH-OLED Current Density [ma/cm 2 ] EQE[%], Power Efficiency [lm/w] Current Efficiency [cd/a] Power Efficiency [lm/w] Luminance [cd/m 2 ] PEDOT (40nm) μ h μ ν 0 Power Efficiency Current Efficiency Luminance Bu-PBD(60nm) LiF 3 (~1nm) Al (0nm) D dm EQE Luminance Current Density [ma/cm 2 ] 00 0 Green PH-OLED C-Effi. : 86.3 cd/a Pow-Effi.: 92.4 lm/w V ti : Lumi. : 40 cd/m 2 CIE(x,y)=(0.32,0.61) EQE : Current Density Alied Voltage [V] Luminance [lm/w]

10 Otical Power Density Otical Power Density Otical Power Density PEDOT (40nm) CBP (20nm) Bu-PBD(0-300nm) LiF 3 (~1nm) Al (0nm) 0% 80% λ:520nm Dissiated Power Density of Each Otical Mode in PH-Green OLED μ h μ ν D dm (b) Horizontal diole Otical Mode Lossy Surface Wave Surface Plasmon (Metal Cathode) Waveguide mode (Thin films) mode (Thick films) (Out-couling) 12% Surface Plasmon & LSW 9% Waveguide mode k LSW k SP k WG k Sub k 0% 80% 60% 40% ~30% 20% 0% 0% 80% (a) Random diole 47% Surface Plasmon loss Lossy Surface Wave 8% Waveguide mode Distance between Diole and Cathode [nm] (c) Vertical diole 22% mode 23% 88% Surface Plasmon loss Lossy Surface Wave 60% 36% mode 60% 6% Waveguide mode 40% 40% 20% 42% 20% 6% mode 0% Distance between Diole and Cathode [nm] 0% Distance between Diole and Cathode [nm]

11 Diole Radiation Processes in OLED OLED Diole non-radiative recombination R nr R SP R ra Inside Radiation radiative recombination S nr γ Surface Plasmon ohmic daming(metal) S ra guided mode absortion direct transmission radiative extraction E ra E SP Outside Radiation Phonon Internal Quantum Efficiency η η int γ Rra γ R R S ra ra Sra S nr nr RSP R SP Radiative extraction of surface lasmon int ra RSP 0 ηnsp R ra R R nr R SP 0 γ 1 Suression of Surface Plasmon Couling Diole kees away from the cathode Multi-cathode structure Re-emission from Surface Plasmon Resonance Nano-size eriodic structure (Diffraction effect by k-matching)

12 PH-OLED with Multi-cathode Structure Multi-Cathode) MgAg (~nm) Otical Buffer Layer (0~300nm) Mirror Ag (0nm) 12

13 PH-OLED with Multi-cathode Structure 1 st. Ste 2 nd Ste 3 rd Ste MgAg (0nm) MgAg (~nm) MgAg (~nm) Otical Buffer Layer (0~300nm) MgAg (~nm) Otical Buffer Layer (0~300nm) Mirror Ag (0nm) Reference Device TOLED TOLED+O.B.L. Multi-Cathode (Normal Cathode) 13

14 Power Density [a.u.]. Surface Plasmon Loss vs. Film Thickness of MaAg Cathode Otical Power Density [%] 0 (c ) MaAg : nm Horizontal Diole (μh) Vertical Diole (μv) TM Waveguide External Plasmon (b) MgAg : 20nm TM Plasmon % Plasmon loss 51% 13% Waveguide 13% 23% 18% 20% 19% 1 0 Thickness of MgAg Cathode [nm] λ:520nm (a) MgAg : 0nm TM Plasmon In-Plane Wave Vector (kh / kair) MgAg (1~0nm)

15 Power Density (a.u.) μ D dm Metal Relation between Back reflection coefficient and surface lasmon loss r ε 0 ε 1 ε 2 ε 3 D dm Dissiated ower in k-sace ω k P // // 8π ε1 kz r r λ:520nm MgAg (5~0nm) // 2 2 k Re μ k 1 r ex2ik d 12 k k Z1 Z1 ε ε SP1 SP2 Reflection coefficient on the cathode surface 2 2 k k Z2 Z2 r12 r23ex 2ik 1 r r ex 2ik ε ε 1 1 Z2 Z2 z t t Re k Z r Z r Imr ex - k 1 y π π/2 Power Sectrum In-lane Wave Vector kh/k0 tan 1 Im r Im r Re r 0nm 50nm 30nm 20nm Surface Plasmon nm 5nm 2 2 k Z k1 k// -π/2 k // x -π Phase shift

16 Phase shift of back reflection coefficient by otical buffer layer μ D dm Metal r Otical Buffer Layer ε 0 ε 1 ε 2 ε 3 D dm Dissiated ower in k-sace ω k P // // 8π ε1 kz r r λ:520nm MgAg (nm) O.B.L (0nm) n=1.0~2.2 // 2 2 k Re μ k 1 r ex2ik d 12 k k Z1 Z1 ε ε SP1 SP2 Reflection coefficient on the cathode surface k k Z2 Z2 r12 r23ex 2ik 1 r r ex 2ik ε ε 1 1 Z2 Z2 t t Re z r k Z Z r Imr ex - k 1 y 2 2 k Z k1 k// π π/2 -π/2 -π Im r Phase shift SPP quenching k // x

17 Power Density [a.u.]. Surface Plasmon Loss vs. Film Thickness of OB-Layer in TOLED Otical Power Density [%] TM Horizontal Diole (μh) Vertical Diole (μv) (c ) d OBL : 80nm Waveguide External TM (b) d OBL : 20nm Plasmon Plasmon loss 8% 42% Waveguide mode 39% 14% 23% mode 32% 19% 21% Thickness of Otical Buffer Layer [nm] (a) without OBL TM Plasmon In-Plane Wave Vector (kh / kair) MgAg (~nm) Otical Buffer Layer (0~300nm)

18 Otical Energy Reduction of Surface Plasmon Loss by Multi-cathode (Normal Glass) Power Density [a.u.]. (n=1.52) MgAg (0nm) (a) Normal Cathode (n=1.52) MgAg (~nm) Otical Buffer Layer (120nm) Mirror Ag (0nm) (b) Multi-Cathode (a) Normal cathode (MgAg:0nm) Surface Plasmon In-Plane Wave Vector (kh / kair) (b) Multi-cathode (n sub :1.52) Horizontal Diole (μh) Vertical Diole (μv) TM Waveguide mode 0% 90% 80% 70% 60% 50% % 54% 12% (Plasmon loss) 28% (Waveguide mode) mode Surface Plasmon % 30% 18% 32% ( mode) 20% % 0% 18% 28% () Distnce between Diole and Cathode [nm]

19 Otical Energy Reduction of Surface Plasmon Loss by Multi-cathode (High refractive-index glass) Power Density [a.u.]. (n=1.52) MgAg (0nm) (a) Normal Cathode High refractive-index Glass (n=1.80) MgAg (~nm) Otical Buffer Layer (120nm) Mirror Ag (0nm) (b) Multi-Cathode (a) Normal cathode (MgAg:0nm) In-Plane Wave Vector (kh / kair) (b) Multi-cathode (n sub :1.52) Horizontal Diole (μh) Vertical Diole (μv) TM Surface Plasmon Waveguide mode 0% 90% 80% Plasmon Loss 12% ~1% (Waveguide mode) mode Surface Plasmon 70% 60% ~50% 50% 40% 30% 20% % 0% 60% ( mode) 27% () Distnce between Diole and Cathode [nm] (c) Multi-cathode (n sub :1.80) External mode mode Plasmon In-Plane Wave Vector (k h / k air )

20 Outut Power Intensity (a.u.) E z -Field of Vertical Diole in FDTD Simulation (a) Normal Cathode (b) Multi-Cathode (n sub :1.52) (c ) Multi-cathode (n sub :1.80) 36% in Glass & (Random Diole) 59% 87% Detector in glass 4.5μm Ez Glass OLED μ ν 14μm Glass OLED Cathode (n=1.52) MgAg (0nm) (n=1.52) MgAg (~nm) Otical Buffer Layer (120nm) High refractive-index Glass (n=1.80) MgAg (~nm) Otical Buffer Layer (120nm) Glass OLED Multi-Cathode Mirror Ag (0nm) Mirror Ag (0nm)

21 EQE [%] Device Performance of Green PH-OLED with High Refractive-index Glass Power Efficiency [lm/w] High refractive-index glass with Half-lens Reference device High refractive-index glass with μ-lens array Current Density [ma/cm 2 ] 00 0 High refractive-index glass with Half-lens High refractive-index glass with μ-lens array Reference device Luminance [cd/m 2 ] Emission (n=1.52) MgAg (0nm) μ-lens Array Glass (n=1.80) MgAg (~nm) Otical Buffer Layer (120nm) Half Ball Lens Glass (n=1.80) MgAg (~nm) Otical Buffer Layer (120nm) Device Efficiencies in green PH-OLED s Device Structure EQE [%] Power Effi. [lm/w] Reference With μ-lens With Half-lens Mirror Ag (0nm) Mirror Ag (0nm)

22 Device Performance of Green PH-OLED with High Refractive-index Inter Layer EQE [%], Power Efficiency [lm/w] Current Efficiency [cd/a] Power Efficiency [lm/w] Luminance [cd/m 2 ] Glass (n=1.52) SEM image High Refractive-Index Inter Layer (n=2.2) MgAg (~nm) Otical Buffer Layer (120nm) Mirror Ag (0nm) Surface Aearance Luminance 000 Current Efficiency 0 00 Power Efficiency 0 EQE Current Density [ma/cm 2 ] 00 With multi-cathode and inter-layer μm High refractiveindex Inter-layer Glass Sub. High-n Inter Layer 0 Reference device With multi-cathode Glass Inter Layer Light Scattering Luminance [cd/m 2 ]

23 Conclusions 1. It was roosed that surface lasmon loss is successfully suressed by using multi-cathode structure consisting of otical comensation layer and semitransarent cathode. Aroximately 80% of otical ower in the diole emission can be converted to glass and air modes in calculation. 2. Phoshorescent green OLED with multi-cathode and high refractive-index medium showed a maximum EQE of 40% in inter-layer, 47% in μ-lens array and 65% in half-ball lens. Power efficiency was imroved by a factor of 1.7 comared with reference device in exeriments. 3. There is a good agreement between EQE in exeriments and light extraction efficiency in calculation from an otical oint of view. Financial Suort High Technology Research Center Program by Ministry of Education, Culture, Sorts and Scientific and Technology in Jaan Grant-in-Aid for Scientific Research (No ) from the Jaan Society for the romotion of Science Mikami Lab. Otical Electro- Magnetic Lab. Kanazawa- Inst.Tech.