Enhanced electron affinity and charge balance property of a bipolar material: highly efficient solution-processed deep blue electrofluorescent and green electrophosphorescent devices

A novel bipolar material featuring triphenylamine and benzimidazole groups has been designed and synthesized. The unique star-shaped configuration enables the materials with high thermal stability and a film-forming property. Both DFT simulation and experimental results demonstrated that the enhanced electron affinity and transporting ability endows the solution-processed devices based on TPA-2PBI with more balanced charge flux and higher exciton recombination efficiency. As a result, the non-doped deep blue electrofluorescent device using TPA-2PBI as the emitter shows the maximum luminance efficiency of 1.53 cd A(-1) and the green electrophosphorescent device using TPA-2PBI as the host material shows the maximum luminance efficiency of 38.0 cd A(-1). Furthermore, the TPA-2PBI based devices exhibit higher performance compared with the corresponding devices based on 2TPA-PBI.