High-Efficiency Blue Phosphorescent Organic Light-Emitting Devices with Low Efficiency Roll-Off at Ultrahigh Luminance by the Reduction of Triplet-Polaron Quenching.

High-performance phosphorescent organic light-emitting devices (PhOLEDs) at high luminance are still a remaining problem that needs to be solved, especially blue PhOLEDs. Here, 5-(5-9 H-carbazol-9-yl)pyridin-2-yl)-8-(9 H-carbazol-9-yl)-5 H-pyrido[3,2- b]indole (p2PCB2CZ) with excellent characteristics as a host is designed to realize a novel host-guest system without hole trapping effect in blue PhOLEDs. The device in which p2PCB2CZ and bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium(III) (FIrpic) is used as host and guest, respectively, is proposed to improve the performances of blue PhOLEDs at high luminance, especially at ultrahigh luminance (>30000 cd/m). The maximum external quantum efficiency (EQE) of this type of blue PhOLEDs is 19.2%, while the maximum EQE of the reference blue PhOLEDs is 18.7%. Nevertheless, the p2PCB2CZ-based devices exhibit significant advantages at high luminance, because its EQE still attains to 10.8% even when the luminance increases to 30000 cd/m, which is 1.67 times that of the reference device. From measurements based on steady-state and time-resolved spectroscopies, the reduction of triplet-polaron quenching in p2PCB2CZ-based devices is proved to be the main reason for improving the performances of blue PhOLEDs at high luminance.