title: Tuning Charge Balance in Solution-Processable Bipolar Triphenylamine-diazafluorene Host Materials for Phosphorescent Devices.
abstract: Three bipolar hosts, namely TPA-DAF, TPA-DAF2, and TPA-DAF3, comprising an electron-donating triphenylamine (TPA) group and electron-accepting 4,5-diazafluorene (DAF) units are investigated for phosphorescent organic light-emitting diodes (PhOLEDs). Given the nonplanar structure of the sp(3)-hybridized C9 atom in DAF unit, these molecules have a highly nonplanar configuration, good film-forming property, and high triplet energy (ET) of 2.88-2.89 eV. Among them, TPA-DAF shows more balanced carrier injecting/transporting ability, suitable highest occupied molecular orbital (MO) energy level and higher current density, and therefore TPA-DAF-based devices exhibit the best performances, having an extremely slight efficiency roll-off with current efficiency of 20.0 cd/A at 973 cd/m(2), 19.5 cd/A at 5586 cd/m(2), and 17.6 cd/A at 9310 cd/m(2) for blue PhOLEDs; 23.5 cd/A at 1059 cd/m(2) and 15.3 cd/A at 8850 cd/m(2) for green PhOLEDs; and 12.2 cd/A at 1526 cd/m(2), 10.5 cd/A at 5995 cd/m(2), and 9.2 cd/A at 8882 cd/m(2) for red PhOLEDs, respectively. The results also provide a direct proof for the influence of charge balance on the device performance.
authors.forename: Zhaokang
authors.initials: Z
authors.lastname: Fan
authors.forename: Huiru
authors.initials: H
authors.lastname: Zhao
authors.forename: Nengquan
authors.initials: N
authors.lastname: Li
authors.forename: Yiwu
authors.initials: Y
authors.lastname: Quan
authors.forename: Qingmin
authors.initials: Q
authors.lastname: Chen
authors.forename: Shanghui
authors.initials: S
authors.lastname: Ye
authors.forename: Shuhua
authors.initials: S
authors.lastname: Li
authors.affiliation: #Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Quli
authors.initials: Q
authors.lastname: Fan
authors.forename: Wei
authors.initials: W
authors.lastname: Huang
keywords: 4,5-diazafluorene; bipolar host; phosphorescent diodes; triphenylamine