High-efficiency blue phosphorescent organic light-emitting devices with low efficiency roll-off at ultrahigh luminance by reduced the triplet-polaron quenching

Ziwei Yu, Jiaxin Zhang, Shihao Liu, Letian Zhang, Yi Zhao, Hongyu Zhao, Wenfa Xie
ACS Applied Materials & Interfaces 2019 January 18
High performance phosphorescent organic light-emitting devices (PhOLEDs) at high luminance are still a remaining problem needing to be solved, especially blue PhOLEDs. Here, 5-(5-9H-carbazol-9-yl) pyridin-2-yl)-8- (9H-carbazol-9-yl) -5H-pyrido [3, 2-b] indole (p2PCB2CZ) with excellent characteristics as 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 ultrahigh luminance (>30000 cd/m2). The maximum external quantum efficiency (EQE) of this type blue PhOLEDs is 19.2%, while the maximum EQE of reference blue PhOLEDs is 18.7 %. Nevertheless, the p2PCB2CZ-based devices exhibit significant advantage at high luminance, because its EQE still attains to 10.8% even when the luminance increases to 30000 cd/m2, which is 1.67 times that of the reference device. From measurements based on steady-state and time-resolved spectroscopy, the reduction of triplet-polaron quenching in p2PCB2CZ-based devices is proved to the main reason for improving the performances of blue PhOLEDs at high luminance.

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