Efficiency enhancement and voltage reduction in white organic light-emitting devices

High-efficiency and low operating voltage fluorescent white organic light-emitting devices (WOLEDs) have been realized by doping either 4,7-diphenyl-1,10-phenanthroline (BPhen) or N,N-'-bis(1-naphthyl)-N,N-'-diphenyl-1,1(')-biphenyl-4,4(')-diamine (NPB) into the blue light-emissive layer. Devices doped with BPhen (or NPB) exhibited a maximum power efficiency of 8.7 lm/W (7.6 lm/W), about 74% higher than that of the reference device (5.0 lm/W). Such performance improvement is ascribed to the incorporation of a better electron-transporting layer and an improved carrier transport through the emissive layer by mixing with the higher drift mobility materials. It provides a simple and general means to improve the power efficiency of WOLED. (C) 2007 American Institute of Physics.