Reducing efficiency roll-off of phosphorescent organic light emitting diodes by using phosphor assisted energy funneling

Abstract

Though phosphorescent emitters have been widely applied in commercialized organic light-emitting diodes (OLEDs), most of them always suffer from severe efficiency roll-off because high exciton concentration at high current density would cause aggravation of triplet-triplet annihilation (TTA) and triplet-polaron quenching (TPQ) effect. Herein, an energy funneling system were formed in phosphorescent OLEDs (PhOLEDs) to relieve the exciton accumulation and further suppress the quenching effects by utilizing a phosphorescent emitter as assistant host. By simply adding blue phosphors to green and red devices, the EQEs of green and red devices at the brightness of 10000 cd m −2 were remarkably improved from 12.8% to 11.1%–20.2% and 22.4% for green and red OLEDs, respectively. The results presented in this work are quite beneficial to OLED display and lighting industry. • The reasons for the sharp decline in efficiency of PhOLED under high brightness are carefully analyzed. • An energy funneling system was proposed for improving the efficiency under high current density. • The EQEs at the brightness of 10000 cd/m2 were remarkably improved from 12.8% to 11.1%–20.2% and 22.4% for green and red PhOLEDs, respectively.