Efficiency Improvement of Iridium Complex Red Phosphorescent Organic Light-Emitting Diodes by Doping Technique

• Main Authors: Lien-Cheng Kao, 高連成
• Other Authors: Meiso Yokoyama
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/36822792924985373938

碩士 === 義守大學 === 電子工程學系碩士班 === 98 === In this Study, the red phosphorescent organic light-emitting diodes (RPHOLED) has been fabricated containing a host of 4,4’-bis(9-carbazolyl)-biphenyl[CBP] and a dopant of Iridium complex bis(1-(phenyl)isoquinoline) iridium (III) acetylanetonate [Ir(piq)2(acac)]. Various doping technique is discussed for optimizing the device’s characteristics. RPHOLEDs with an uniformly doped emission layer are fabricated. When the doping concentration of Ir(piq)2(acac) in CBP reaches 15 wt%, the device exhibits the maximum luminance of 16700 cd/m2 at 16.1V, and the maximum luminous efficiency of 6.3 cd/A at 10 mA/cm2. The CIE coordinates (x,y) of the device is (0.67, 0.32). Unlike commonly uniformly doped emission layer, experimental results demonstrate that electroluminescent efficiency can be improved by changing doping profile of Ir(piq)2(acac) in CBP of the RPHOLED device. By examining the changes of recombination zone and current density in a partially doped emission layer, we find that most of the hole/electron recombination occurs at the emission layer close to the hole blocking layer. Hole injection and transporting ability and path can be improved if an appropriate doping concentration exists at the emission layer close to the hole transporting layer. RPHOLEDs with a stepwise doped emission layer are successfully fabricated. The structure of the device is ITO/m-MTDATA(30nm)/NPB(10nm)/CBP:Ir(piq)2(acac)(7 wt%)(20nm)/CBP:Ir(piq)2(acac)(15wt%)(10nm)/Bphen(10nm)/Alq3(30nm)/LiF(1nm)/Al. It shows the maximum luminance of 38700cd/m2 at 14V, and the maximum luminous efficiency of 10.33cd/A at 9mA/cm2. The CIE coordinates (x,y) of the device is (0.67, 0.32) and the color purity is 99.74%, which meets the need of red light-emitting requirements in the full color flat-panel display