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1 Theories and Applications of Chem. Eng., 2004, Vol. 10, No 유기 EL 개발동향및소자특성개선을위한디바이스물리현상해석 진병두 Corporate R&D Center SAMSUNG SDI

2 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Contents OLED features - Electroluminescent Process - PM & AMOLED - SDI s R&D for AMOLED Layered Structure/ Charge Balance of OLED - Doping/ Energy Transfer - Optical / Physical Properties of OLED device Design for Optimum OLED Device - Charge Mobility Control/Modified Cathode - Doping Control Technical Issues for Color Patterning - Shadow Mask/ Inkjet/ Laser Patterning

3 Theories and Applications of Chem. Eng., 2004, Vol. 10, No OLED : Features Small Molecular OLED Cathode Electron Transport Layer Emission Layer Hole Transport Layer Hole Injection Layer Anode Glass substrate Polymer OLED Cathode Emission Layer Hole Transport Layer Anode Glass substrate Superior viewing performance: emissive bright colors, wide viewing angle, fast response time, and high contrast Enabling form factor: Thin, light-weight, rugged, and conformable Excellent operating characteristics: low operating voltage, power efficient, and wide temperature range Low cost: simple processing, vacuum deposition, inkjet printing, spin coating, roll-to-roll (web) processing

4 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Electroluminescent Process Luminescence Internal quantum efficiency: η int = γ r st φ Nonrad. - (T* + S*) + hν Charge transport (Hopping) γ is ratio of number of exciton formation events within device to number of electrons in external circuit. r st is fraction of excitons formed as singlets φ is efficiency of radiative decay of excitons (in the device structure -depends on photonic structure) External quantum efficiency: η ext (1 / 2n 2 ) η int

5 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Singlet state (S) spin : s i = +1/2, -1/2 the total spin quantum number : S = Σ s i = 0 the spin multiplicity : M = 2S + 1 = 1 Triplet state (T) spin : s i = +1/2, +1/2 or -1/2, -1/2 the total spin quantum number : S = Σ s i = 1 the spin multiplicity : M = 2S + 1 = 3 α 1 2 β α 1 α 2 β 1 2 β β α α 1 2 β α β E ground state (singlet state) singlet excited state triplet excited state

6 Theories and Applications of Chem. Eng., 2004, Vol. 10, No PMOLED vs AMOLED Structures Cathode Scan Line Data Line Source Gate Drain Anode 구동법 Panel 크기소비전력 IC Cost Passive Matrix Duty 구동 (Rolw line 선택시점등 ) Size: < 2 이하소형 해상도 : < 현재 240 line 높은순간휘도, 고전압구동 (>12V) 높은소비전력 구동 IC 외장 단순구조로공정비용낮음 투자비낮음 Active Matrix Static 구동 ( 상시점등 ) Row line 수에관계없이고휘도 실현가능 저전압구동가능 (~8V) 구동회로 Panel 내부내장 저온 poly Si TFT+OLED 고비용구조 투자비높음

7 Theories and Applications of Chem. Eng., 2004, Vol. 10, No PM 과 AM 의소비전력비교 소형영역 : PM/AM OLED 가투과형 (STN/TFT)LCD 보다경쟁우위 10 消 1 費電力 (W) 0.1 중형영역 : AM OLED가투과형 TFT LCD보다경쟁우위 OLED(PM) PM OLED< 투과형LCD 투과형 TFT LCD OLED(AM) 투과형 STN LCD 반사형 TFT LCD AMOLED< 투과형 LCD 0.01 AMOLED OLED< 반사형 LCD Size(Inch) OLED는 30% 점등, 6이하QVGA, 7 이상VGA(2002예상 )

8 Theories and Applications of Chem. Eng., 2004, Vol. 10, No AMOLED R&D History Samsung SDI s Development of AMOLED

9 Theories and Applications of Chem. Eng., 2004, Vol. 10, No The Role of Each Layer in OLED low work function metals Li(2.9eV), Ca(2.9eV), Mg(3.7eV) too reactive with oxygen and moisture Double layer or mixed layer structure (Ca/Al, Li:Al, Mg:Ag) Insulator/metal structure (LiF/Al, CsF/Al, BaF 2 /Al, LiF/Ca/Al) Metal-organic complex(alq 3, Gaq 3..) Electron transport Hole blocking Host-dopant system(alq 3 :DCJTB..) Energy transfer from host to dopant Fluorescence and phosphorescence Light emitting Color tuning Amine type materials Hole transport(high hole mobility) Electron blocking ITO or IZO transparent electrode low surface roughness high work function : UV/ozone, plasma Amine type materials, CuPc intermediate work function btw anode and HTL Enhance injection efficiency of holes from anode Good contact with anode Smoothening effect on ITO

Theories and Applications of Chem. Eng., 2004, Vol. 10, No. 2 2854 Charge Balance Issue Single-layer devices Hetero-structure (Multilayer) Unbalanced carrier injection Lower efficiency.

10 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Charge Balance Issue Single-layer devices Hetero-structure (Multilayer) Unbalanced carrier injection Lower efficiency. For Improving Charge balance Balanced carrier injection Band offsets between the layers/ space charges build up at heterojunction. improved efficiency 1) Carrier Injection (balanced injection; N e =N h ) 2) Carrier Transport (bipolar transport; m e = m h ) 3) Electron-hole recombination and exciton formation 4) Radiative and non-radiative recombination of excitons and energy transfer

11 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Doping: Energy Transfer Processes

12 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Evaluation of OLED devices QUANTITY power power per unit area power per unit solid angle power per area per solid angle RADIOMETRIC watt (W) W/m 2 W/sr W/m 2 -sr PHOTOMETRIC lumen (lm) lm/m 2 = lux (lx) lm/sr = candela(cd) lm/m 2 -sr = cd/m 2 = nit

hole/electron mobility : for Mobile charge distribution and

Mobility in the bulk d ~ 100 nm luminescent polymers FET Mobility

13 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Physical/Electrical Properties : Mobility - Measurement of hole/electron mobility : for Mobile charge distribution and balance optimize TOF Mobility in the bulk d : 1~5 µm Transient EL Mobility in the bulk d ~ 100 nm luminescent polymers FET Mobility in a thin layer d ~ 50 nm τ = 2 d µ V d 2 µ = V τ Not reliable for Inrinsic mobility

14 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Design for Optimum OLED : Control of Mobility Blue polymer + small molecule HTLs - Lower driving voltage Optimal composition for efficiency/lifetime (Chin et al., APL 2004) - No exciplex formation between blue LEP/HTL (Suh et al. Adv. Matl. 2003) Brightness (Cd/m2) Applied Bias (V) BJ Contour plot 0.8 : Power efficiency 1 (lm/w) TDAPB PANa

15 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Measurement of Time-of-Flight Mobility - Emission Layer with 3-component mixture anode PEDOT:PSS vac.level TDAPB Blue LEP x10-5 photocurrent (A.U.) photocurrent (A.U.) 1.0 BJ (neat) 0.8 BJ/TDAPB/PANa 5/2/2 BJ/TDAPB/PANa 4/4/ t (sec) t(sec) Mobility (cm 2 V -1 s -1 ) BJ (neat) BJ/TDAPB/PANa 5/2/2 BJ/TDAPB/PANa 4/4/ E 1/2 (V/cm 2 ) 1/2

16 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Design for Optimum OLED : Modified Cathode Modified Cathode : LiF, LiF/Ca for Electron Injection lower built-in potential ; Shaheen et al. JAP 84, p2324 (1998) efficient electron injection ; Brown et al. APL 79, p174 (2000) Thickness of LiF affects leakage current at reverse bias Thermal treatment at higher temperature : Improving Lifetime Leakage Current (ma/cm LiF 6nm 170 C LiF 6nm 130 C LiF 3nm 170 C LiF 3nm 130 C reduced leakage current Applied Bias (V) Brightness (% (Chin et al. APL 2004, accepted) LiF 6nm 170 C LiF 6nm 130 C LiF 3nm 170 C LiF 3nm 130 C Elasped time (hr)

17 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Design for Optimum OLED : Doping Control - Graded doping ratio at emission at Emission layer : Profile for maximum efficiency is depends on charge carrier mobility, energy level of host/dopant combination Luminance (Cd/m 2 ) % 7% 10% 10/7/4% 4/7/10% Applied Bias (V) Green Phosphorescent device Efficiency (lm/w) Cathode ETL BL 4% 7% 10% HTL Anode ( ITO) (a) EML (doping %) Cathode ETL BL 10% 7% 4% HTL Anode ( ITO) (b) - P-I-N Doping at transport layers : Ohmic contact to electrodes HTL p-doping/ ETL n-doping

18 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Color Patterning Technology Small Molecule OLED : Shadow Mask Current Status (400x400mm 2 기준 ) : about 120 ppi Near Future : over 150 ppi > 250ppi (Required Shadow Mask Improvement) Pixel-Pixel Align Margin (LCD <20 μm ) Items Current Status (Gen II Evaporator) Shadow Effect Pixel Pitch Variation Total Pitch Variation < 5 μm ±~10 μm ±~10 μm Pixel-Pixel Align Margin: ~35 μm over 150ppi?? (Pixel Pitch <60 μm ) Substrate Fine Metal Mask Alignment Accuracy <±5 μm Source

Challenges : Performance Degradation after Printing Repeatability of Ink-Jet Printing Non-uniformity of the coated film

19 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Inkjet Printing (Polymer OLED) Advantages : Simple Process, Small Usage of Material High Resolution, Large Size Challenges : Performance Degradation after Printing Repeatability of Ink-Jet Printing Non-uniformity of the coated film µm Nozzle Nozzle plate Ligament Main Drop All drop ligaments pulled in to main drop, typically 80 ms after ejection W ITO Passivation TR Units Glass Substrate Bank T Insulator Layer

transfer layer as EML (Small molecule, Hybrid, Polymer) - Multilayers, Flexible display (Roll-to-Roll process) High

20 Theories and Applications of Chem. Eng., 2004, Vol. 10, No LITI (Laser Induced Thermal Imaging) Advantages: Scalability to Large-size Glass Dry Patterning Process - Various transfer layer as EML (Small molecule, Hybrid, Polymer) - Multilayers, Flexible display (Roll-to-Roll process) High Resolution - Alignment Accuracy < ±2.5 Micron Substrate Donor Film Laser Beam Laser 17 UXGA LITI AMOLED (presented at SID 2004) Donor Film LTHC adhesion LEP cohesion adhesion Substrate

21 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Encapsulation for Future Devices 박형봉지기술 기존 TFT- LCD 기존 OLED 박형 OLED Flexible OLED 상판 Glass TFT Glass Back Light 봉지용 Glass TFT Glass 봉지용초박막 TFT Glass 봉지용초박막 Flexible TFT Glass mm 0.2mm Weight Thickness Breakage Cost 20 grams 5 mm 10% $18.00

22 Theories and Applications of Chem. Eng., 2004, Vol. 10, No Summary/ Conclusion AMOLED : very promising for Ideal Mobile, TV, and Perfect Future Displays. More Improvement of OLED Technologies is Essential to Meet Requirements of Various Application. - OLED lifetime issue - Color patterning : for large size manufacturing - Thin/light display: next-generation encapsulation Analytic Methods : for Device Characterization - Optical characterization for luminance/efficiency - Physical/electrical characterization : carrier mobility/transient measurement Methods to Boost Luminous Efficiency & Lifetime - Facilitate charge injection by optimized device design - Balancing charge transport at OLED : most important factor to harvest maximum lifetime

유기 발광 다이오드의 전하주입 효율 향상을 통한 발광효율 향상 연구

유기 발광 다이오드의 전하주입 효율 향상을 통한 발광효율 향상 연구 - i - - ii - - iii - - iv - - v - - vi - 그림차례 - vii - - viii - - 1 - 5). - 2 - - 3 - 유기발광다이오드 ( 고분자또는저분자 ) 무기발광다이오드 (p-n junction LED) - + cathode ETL EML HTL HIL anode 발광 두께 : 100 ~ 200 nm 양극 ( 투명전극,