High quantum efficiency in simple blue phosphorescent organic light-emitting diodes without any electron injection layer

High efficiency simple blue phosphorescent organic light-emitting diodes (PHOLEDs) without any electron injection layer were developed using a spirobifluorene-based phosphine oxide (SPPO13) as a host material in the emitting layer. A high quantum efficiency of 20.3% was obtained from the SPPO13 device, with a common device structure and quantum efficiency of 19% achieved in the simple blue device without any LiF electron injection layer. Efficient electron injection from the Al cathode to the SPPO13, without any electron injection layer, was responsible for the high quantum efficiency in the blue PHOLEDs.