Combination of LiF Light Extraction Layers and SiO2 Nanoparticles Scattering Layers for Green Organic Light-emitting Diodes

• Main Authors: KUO, WEI-LI, 郭韋利
• Other Authors: YANG, SU-HUA
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/2edzw9

碩士 === 國立高雄科技大學 === 電子工程系 === 107 === In this study, we mainly focused on the light extraction technology. The green light organic light emitting diode (OLED) combined with the light extraction technology was used to increase the optical efficiency by adding the lithium fluoride light extraction layer, the silica nanoparticle scattering layer and the grinding glass. Firstly, a green light-emitting organic light-emitting diode with simple structure was prepared. The peak wavelength was 520 nm and the luminance was 8,800 cd/m2. In the first part, lithium fluoride (LiF) is used as the light extraction layer of OLED's external structure, and the effect of LiF on the performance of OLED with different thickness was discussed. The light extraction ability of LiF is observed. When the thickness of LiF reaches 5 nm, the efficiency increases to the maximum value. If the thickness increases again, the efficiency of the components will decrease. In this part, the luminance of the device was improved 28.4%, and other efficiency was also improved. In the second part, the rough glass substrate is used as the scattering layer. The scattering effect is produced by random rough surface, it can extracted light. In this part, the characteristics of light extraction are discussed through the rough glass substrate with different grinding time. It was found that when the grinding time is 135 seconds, the component efficiency reaches its optimum level. It was also observed that when the grinding time was longer, the light can not extracted easily because of the deeper rough surface structure. At this part, the luminance of the device was improved 34%, and other efficiency was also improved. The third part combines the best results of the first two parts and compares the improved of efficiency of the device. The first part has the optimum thickness of LiF light extraction layer at 5 nm, while the second part has the optimum time of grinding 135 seconds of rough glass. After combining the two optimum structures, it is observed that the efficiency of the device is higher. In this part, the luminance of the device was improved 43.2%, and the efficiency of other items was also improved. In the fourth part, negative transparent photoresist was used as the host material of the scattering layer, and different concentrations of silica were doped as nanoparticles in the scattering layer, and their scattering ability was observed and compared. When the nanoparticles reach a certain concentration, the scattering ability is the best. If the concentration increases again, the efficiency of the device will decreased. Because the refractive index of SiO2 is 1.46 between air and glass, the refractive index matching structure of the device will be formed. Therefore, the best concentration of SiO2 nanoparticles will be used in the last part. In this part, the luminance of the device was improved 45.5%, and other efficiency was also improved. In the last part, this part is the optimum structures combining all the above experimental conditions and then comparing the changes of the overall efficiency of the device. It was observed that the luminance was improved 55.6%, and other efficiencies were significantly improved. The green light organic light emitting diode with high light extraction efficiency was realized.