Enhancement in efficiency of blue-green polymer light emitting diodes with a double-blocking layer structure

• Main Authors: Dao-Wu Zhuang, 莊道武
• Other Authors: Su-Hua Yang
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/25088204106644490420

碩士 === 國立高雄應用科技大學 === 電子與資訊工程研究所碩士班 === 96 === We demonstrated the properties of blue-green polymer light-emitting diodes (BGPLEDs). In the device configuration of ITO/PEDOT:PSS (9000 rpm)/PVK (7000 rpm) /PFO:OPA3008 (0.7 wt%, 4500 rpm)/BCP (0.2 nm)/Alq3 (10 nm)/LiF (2.5 nm)/Al (150 nm). By changing the spin speed for the PEDOT:PSS coating, a better charge balance result in the recombination zone and a improved a performance could be obtained. An PVK layer was use as an electrons blocking and holes transporting layer. The Alq3 is used to as the help electron injection into the PFO:OPA3008 layer from the Alq3 layer and to hinder holes injection into the electron transporting layer. The poly(9,9-dioctylfluorenyl-2,7-diyl) end capped with N,N-Bis (4-methyl-phenyl)-4-aniline (PFO) was a blue emission host material and the poly[(9,9-Dioctyl-2,7-bis(2-cyano)vinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)] (OPA3008) was a green guest material. In this study, the OPA3008 was doped into the PFO layer to obtain blue-green emission. We found the optimum doping ratio was 0.7 wt% of OPA3008 doped in PFO layer, and in this condition, an effective the best energy was transferred from PFO to the OPA3008. CIE coordinates of the device were x = 0.21, y = 0.29. The maximum luminance was 1650 cd/m2 at 9 V and the maximum current efficiency was 1.99 cd/A at 8 V. By introducing a BCP hole blocking layer, the overall performance of the device with a double-blocking structure was significantly improved; the maximum luminance and maximum current efficiency reached 1650 cd/m2 at 10V and 2.85 cd/A at 8 V, respectively.