Highly efficient green single-emitting layer phosphorescent organic light-emitting diodes with an iridium(III) complex as a hole-type sensitizer

In this study, we report a high performance electroluminescent (EL) device based on a green light-emitting iridium complex tris(2-(4-tolyl)phenylpyridine)iridium Ir(mppy)3 by employing another iridium(III) complex tris(phenylpyrazole)iridium Ir(ppz)3 as the sensitizer. Due to the high-lying energy levels of Ir(ppz)3, the co-doped Ir(ppz)3 molecules within the light-emitting layer function as hole trappers, which are beneficial in broadening the recombination zone and facilitating the carriers' balance on the emitter molecules. In addition, the experimental results demonstrated that the co-doped Ir(ppz)3 molecules also function as the ladders of energy transfer between the host and emitter molecules. Consequently, the co-doped devices displayed a slower efficiency roll-off and higher EL efficiencies compared with those displayed by the reference device because of improved recombination probability and suppressed exciton quenching. Finally, the 0.6 wt% co-doped device with a single light-emitting layer achieved the maximum brightness, external quantum efficiency, current efficiency and power efficiency of up to 121000 cd m−2, 31.8%, 111.0 cd A−1 and 101.6 lm W−1, respectively. Even at a high brightness value of 10000 cd m−2, external quantum efficiency and current efficiency as high as 29.2% and 102.0 cd A−1, respectively, can still be retained.