Simple high efficiency red phosphorescent organic light-emitting diodes without LiF electron injection layer

Simple high efficiency red phosphorescent organic light-emitting diodes (PHOLEDs) without any electron injection layer were developed using a phosphine oxide derivative as a triplet host and electron transport material. Electrons could be directly injected from the Al cathode to the phosphine oxide type material. A high quantum efficiency of 12.5% and a high power efficiency of 12.7 lm W^-1 were achieved in the red PHOLEDs without any electron injection layer. In addition, the red PHOLED without any electron transport and electron injection layer also showed a high quantum efficiency of 10.5% and a power efficiency of 10.2 lm W^-1.