Efficiency Improvement of Red Organic Light Emitting Diodes by a Hole Blocking Layer

• Main Authors: Cheng-Wei Ou, 歐正偉
• Other Authors: Meiso Yokoyama
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/00256784253602265132

碩士 === 義守大學 === 電子工程學系 === 92 === Organic light-emitting devices (OLEDs) have attracted much attention due to their potential applications in flat-panel displays. After one decade of intensive research, the green OLEDs with high luminance, high efficiency, saturated emission and practical lifetime have been developed. However, performances of the red OLEDs are still much behind that of the others. The red OLEDs play a decisive in the full-color display, so it is an important topic to improve the properties of red OLEDs. We report the efficiency improvement of red OLEDs by a hole-blocking layer in this study. There are two parts in this work. First, we discuss the effect of TPBi in green OLEDs. The devices structures are ITO/ m-MTDATA(15 nm)/ NPB(60 nm)/ Alq(X nm)/ TPBi(Y nm)/ Alq(60-X-Y nm)/ LiF(0.7 nm)/ Al(20 nm). The characteristics of the device are studied by changing the thickness of the TPBi and Alq layer. We found the devices with 5nm Alq and 2.5nm TPBi possess the optimum properties. The maximum luminescence efficiency can be increased form 4.44 cd/A to 5.63 cd/A, and the maximum luminescence can be increased form 4620 cd/m2 to 5870 cd/m2. Then, we doped DCJTB to fabricate red OLEDs. The devices structure is ITO/ m-MTDATA(15 nm)/ NPB(60 nm)/ Alq:DCJTB(5 nm)/ TPBi(2.5 nm)/ Alq:DCJTB(22.5 nm)/ LiF(0.7 nm)/ Al(20 nm). When the doping concentration of DCJTB is 2wt%, the maximum luminescence efficiency and luminescence can be increased from 3.6 cd/A to 4.63 cd/A and 748.8 cd/m2 to 963cd/m2, respectively. When the doping concentration of DCJTB is 4wt%, the maximum luminescence efficiency and luminescence can be increased from 1.56 cd/A to 2.81 cd/A and 324.5 cd/m2 to 584.5cd/m2, respectively.