Effects of hole injection layer on performance of green OLEDs based on flexible ITO

Abstract

Hybrid 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile(HAT-CN)/molydium oxide (MoO3) is employed as hole injection layer (HIL) to modify the flexible ITO anode in bis(2-phenylpyridine)(acetylacetonate)iridium (Ir(ppy)2acac)-based green phosphorescence flexible organic light-emitting devices (FOLEDs). The hybrid HAT-CN/MoO3 leads to high hole injection efficiency and improvement in device performance. The device with HAT-CN(5 nm)/MoO3(1 nm) as HIL shows a turn-on voltage of 3.0 V, a maximum current efficiency (CEmax) of 41.29 cd/A and maximum power current efficiency (PEmax) of 15.92 lm/W, indicating the maximum efficiency increase by 41.6% and 53.1% compared with that of the single MoO3 as HIL, respectively. The smooth current injection can be achieved by the HAT-CN's ability of cleaning ITO surface. The hybrid HAT-CN/MoO3 reduces the hole injection barrier and suppresses the space change accumulation in electrode/organic layer interface to enhance hole injection efficiently. Our work suggests that the effective modification for flexible ITO anode is necessary to obtain high-efficiency FOLEDs.