| Summary: | 碩士 === 國立虎尾科技大學 === 光電與材料科技研究所 === 94 === This study is mainly divided into two topics to discuss flexible organic light emitting diodes (OLED). The first topic used fluorescent dopants. The other used phosphorescent dopants. First, the research employs a way of spin-coating α-NPD (firstly solved in THF) on ITO surface as an anode buffer layer. The purpose is to reduce the ITO surface roughness and improve the cohesion between ITO and organic materials and then increase the life-time of flexible OLEDs. Compared with thermally evaporated method, the structure: ITO/α-NPD(0.08 wt% in THF)/NPB(20nm)/Alq3(80nm)/LiF/Al can improve the luminance from 516 to 2370 cd/m2 at 10V. In the life-time comparison, the spin-coated buffer layer can also improve the life-time from 621 to 4193 minutes. Then the research utilized CuPc/m-MTDATA double buffer layers to improve the characteristics of flexible OLED. The purpose is to reduce the barrier between ITO and NPB. The thickness of each layer was adjusted. In the optimum structure, ITO/CuPc (10nm)/m-MTDATA(20nm)/NPB(40nm) /Alq3(80nm)/LiF/Al, the maximum luminance is 1820 cd/m2 at 10V and the maximum luminance efficiency is 6.35 cd/A at 9V.
The second topic is the phosphorescent organic light emitting diodes. The thickness of each layer was adjusted. First, the research employed NPB as hole transport layer. The optimum structure is ITO/NPB(50nm)/ CBP:Ir(ppy)3(40nm)/BCP(10nm)/Alq3(50nm)/LiF/Al. The structure achieved the maximum luminance of 10220 cd/m2 at 10V and maximum luminance efficiency of 30.4 cd/A at 6V. And then LiF was replaced with CsF. The maximum luminance efficiency was increased to 32.5 cd/A at 5V. Next this research utilizes TPBi to replace BCP. When the thickness of TPBi is 10 nm, the maximum luminance is 10680 cd/m2 at 10V and maximum luminance efficiency is 34.2 cd/A at 5V. Finally the research utilized α-NPD as hole transport layer and inserted NPB (solved in THF) as buffer layer above the anode layer. The optimum structure is ITO/NPB (0.2wt% in THF)/α-NPD (30nm)/CBP:Ir(ppy)3(50nm)/BCP(20nm)/Alq3(80 nm)/LiF/Al. This structure can obtain a maximum luminance of 8040 cd/m2 at 10V and maximum luminance efficiency of 21 cd/A at 6V. Then the BCP was replaced with TPBi as hole blocking layer. When the thickness of TPBi is 10 nm, the maximum luminance is 12030 cd/m2 at 10V and maximum luminance efficiency is 24.4 cd/A at 7V. By using NPB solved in THF as anode buffer layer, the device life-time can be improved from 151 to 1352 minutes.
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