3,3′-Bicarbazole-based compounds as bipolar hosts for green and red phosphorescent organic light-emitting devices

Abstract

Two 3,3‘-bicarbazole derivatives, with triphenylsilyl and toluenesulfonyl moieties attached to 9,9‘-positions were synthesized and their properties were studied. The compounds exhibited high triplet energies of 2.9 eV which made them useful for efficient triplet exciton harvesting. The compound containing triphenylsilyl moieties was found to have bipolar charge-transporting properties which makes it a good candidate for employment as a host in phosphorescent organic light emitting diodes. A series of green and red devices with the newly synthesized host and phosphorescent emitters were fabricated and the performance of the hist was compared with that of 1,3-bis(N-carbazolyl)benzene (mCP). Triphenylsilyl-substituted 3,3‘-bicarbazole was found to be competitive host with the widely used host mCP. Green and red phosphorescent organic light emitting diodes containing this host showed maximum external quantum efficiencies of 13.8 and 7.7%, respectively.