Di(biphenyl)silane and carbazole based bipolar host materials for highly efficient blue phosphorescent OLEDs

In this paper, a series of new bipolar blue host materials has been designed and synthesized by incorporating dimethyl or diphenyl silane core with connection of carbazole di(biphenyl) groups at different linking positions. The triplet energies and charge-transporting properties of these bipolar host compounds are controlled by restricting or enhancing the conjugation length among silane, biphenyl, and carbazole units. All materials exhibit good thermal/morphological stabilities. Among these host molecules diphenyldi(4-(3,5-bis-carbazol-9-yl)phenyl)phenyl silane (DM4CzDBPSi) showed the highest triplet energy (2.82 eV) and glass transition temperature (197 °C) along with optimal bipolar charge-transporting property. A phosphorescent blue organic light-emitting diode with DM4CzDBPSi silane host and FIrpic dopant system demonstrated best device performances with maximum external quantum efficiency of 20.9% and a power efficiency of 41.28 lm/W.