투명 OLED용 전하주입 및 표면개선 층에 대한 연구

다국어 초록 (Multilingual Abstract)

Transparent organic light emitting diodes (OLEDs) are nowadays recognizing new technology for advanced display. This technology can appear as an ordinary window which allows a clear view of everything behind. Transparent OLEDs have only transparent component (substrate, anode, organic, cathode). Among them, transparent electrodes are very important component because it decides transmittance of devices as well as device performances.
Among the structure of transparent electrodes, the most competitive candidate is thin metal layer with functional layers to improve transparency and resistance. In case of thin metal layer structure, it is important to get a good morphology of thin metal film in improving transmittance and resistance because all of electrical and optical characteristics are affected by the thin metal layer.
In this study, two efficient electron-injecting materials are found and the surface-modifying mechanism by EIL was demonstrated and highly transparent OLED introduced the EIL was investigated.
A lot of materials were introduced as EIL and we found good materials which enhance the transmittance and sheet resistance of electrode by improving Ag surface morphology. This enhancement of surface morphology is because of the formation of Ag oxide between EIL and Ag film. EIL has a role as nucleation seed for forming closed film quickly by interacting with Ag. The Ag oxide seems to behave as a buffer layer and enhanced the surface morphology of Ag film. These characteristics were shown on LiMn2O4, Li2CO3 which containing oxygen inner molecule. When we apply these materials as transparent cathode, transmittance at 550 nm is 90.6%, 91.2%, respectively. Sheet resistance is 5.4 Ω/□.
We fabricated transparent OLEDs with LiMn2O4 or Li2CO3 EIL. Luminance ratio of bottom emission and top emission is 2.1 : 1 which correspond to LiMn2O4 device, 2.0 : 1 which correspond to Li2CO3 device, and CIE color coordinate of bottom emission and top emission is rarely changed. Transmittance of full device of LiMn2O4 and Li2CO3 device is 90.6% and 91.2% respectively.
To reduce sheet resistance of transparent cathode, we increased thickness of Ag film of Li2CO3 device from 12 nm to 17 nm. Then, sheet resistance of the transparent cathode is 2.9Ω/□, and transmittance is 80.9%. As a result of applying the transparent cathode, luminance ratio of bottom emission and top emission is 3.15 : 1, and CIE color coordinate of bottom emission and top emission is rarely changed. Transmittance of full device is 63.5%.

목차 (Table of Contents)

• 1.서 론 1
• 1.1.연구 배경 1
• 1.2.투명 전극 연구 동향 4
• 1.2.1.WO3/ITO 구조 5
• 1.2.2.Ca/Ag double layer 7
• 1.2.3.Dielectric / metal / dielectric 구조 8
• 1.2.4.EIL / metal / dielectric 구조 10
• 1.3.연구 동기 12
• 2.실험방법 13
• 2.1.소자 제작 방법 13
• 2.1.1.기판 세정 13
• 2.1.2.Organic / Metal layer 증착 14
• 2.1.3.Encapsulation 15
• 2.2.측 정 17
• 2.2.1.박막의 두께 측정 17
• 2.2.2.면저항 측정 18
• 2.2.3.투과도 측정 18
• 2.2.4.EM(Scanning Electron Microscope) 측정 18
• 2.2.5.XPS(X-ray Photoelectron Spectroscopy) 측정 18
• 2.2.6.투명 OLED 소자의 특성 평가 19
• 3.결 과 21
• 3.1.Thin metal layer에 적용할 금속 물질 선정 21
• 3.2.EIL 물질 선정 22
• 3.3.EIL에 따른 투명 음극의 투과도 및 면저항 26
• 3.4.SEM을 이용한 Ag 박막 분석 30
• 3.5.XPS를 통한 EIL과 Ag 계면 특성 연구 33
• 3.5.1.LiF와 Ag의 계면 특성 분석 34
• 3.5.2.LiMn2O4와 Ag의 계면 특성 분석 36
• 3.5.3.Li2CO3와 Ag의 계면 특성 분석 38
• 3.6.EIL에 따른 Ag박막의 morphology 개선 효과에 대한 고찰 40
• 3.7.투명 OLED 소자 최적화 및 특성 분석 42
• 3.7.1.LiMn2O4와 Li2CO3의 두께 최적화 42
• 3.7.2.투명OLED 소자의 J-V, L-V 특성 분석 45
• 3.7.3.투명OLED 소자의 투과도 분석 50
• 3.7.4.투명OLED 소자의 J-L 및 효율 분석 52
• 3.7.5.투명OLED소자의 색좌표 및 발광 스팩트럼 분석 56
• 3.8.저저항 투명 OLED 소자 최적화 및 특성 분석 61
• 3.8.1.저저항 투명전극 개발을 위한 Ag박막의 두께 최적화 61
• 3.8.2.저저항 투명OLED 소자의 투과도 특성 분석 62
• 3.8.3.저저항 투명 OLED 소자의 J-V, L-V 특성 분석 65
• 3.8.4.저저항 투명OLED 소자의 J-L 및 효율 분석 67
• 3.8.5.저저항 투명OLED소자의 색좌표 및 발광 스팩트럼 분석 69
• 4.결 론 72
• 참고문헌 74
• Abstract 77