Benzimidazole–carbazole-based bipolar hosts for high efficiency blue and white electrophosphorescence applications

Abstract

A series of novel bipolar blue phosphorescent host materials mBICP, mBINCP and mBIPhCP have been designed and synthesized, which comprehensively outperform the widely used phosphorescent host, 1,3-di(9H-carbazol-9-yl)benzene (mCP). The thermal, photophysical and electrochemical properties of these host materials were finely tuned through linking different carbazole moieties to the benzimidazole. mBICP (T_g = 84 °C) and mBIPhCP (T_g = 103 °C) exhibit high morphological stabilities in comparison with mCP. Theoretical calculations show that the HOMO/LUMO orbitals of these materials are mainly dispersed on the electron donating and electron accepting groups, respectively. A blue PhOLED device fabricated using mBICP as the host exhibits a maximum external quantum efficiency (η_EQE,max) of 18.7% and a maximum power efficiency (η_P,max) of 33.6 lm W⁻¹. Interestingly, the external quantum efficiencies (η_EQE) are still as high as 17.1% at a high luminance of 1000 cd m⁻². Furthermore, the two-color, all-phosphor and single-emitting-layer white device hosted by mBICP achieved a maximum external quantum efficiency (η_EQE,max) of 20.5% corresponding to a maximum power efficiency (η_P,max) of 53.3 lm W⁻¹.