New carbazole-based bipolar hosts for efficient green phosphorescent organic light -emitting diodes

In this work, two new bipolar host materials 3-(5-(9H-carbazol-9-yl)-4'-(1-phenyl-1H-benzo[d]imidazole-2-yl)-[1,1′-biphenyl]-2-yl)-9- phenyl-9H-carbazole (BCZ-PBM) and 3-(5-(9H-carbazol-9-yl)-3'-(4,6- diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-2-yl)-9-phenyl-9H-carbazole (BCZ-TRZ) were designed and synthesized by introducing benzimidazole and triazine groups as acceptor units with carbazole as the donor unit. These two compounds have excellent thermal stability with a high glass transition temperature (Tg > 160 °C) and thermal decomposition temperature (Td > 450 °C). Green phosphorescent organic light-emitting devices (PHOLEDs) D1 and D2 were obtained by doping Ir(ppy)3 into BCZ-PBM and BCZ-TRZ, in which BCZ-PBM based device D1 revealed better performance with an external quantum efficiency (EQE) of 20.4%, maximum current efficiency (CE) of 69.3 cd/A, and maximum power efficiency (PE) of 54.8 lm/W. Notably, the BCZ-PBM-based device exhibited excellent efficacy stability and a low efficiency roll-off of 1.7% at 1000 cd/m2 and 4.7% at 5000 cd/m2. © 2020 Elsevier B.V.