A Novel Bipolar Host Material Based On Carbazole And 1,3,5-Triazine With An Extremely Low Efficiency Roll-Off For Green Pholeds

In this contribution, a novel bipolar host material, namely CzTrz, consisting of a phenylcarbazole for hole transport and a diphenyltriazine for electron transport, was synthesized and investigated. Besides, a carbazolebased unipolar host BCz2 was designed as a reference. Both CzTrz and BCz2 display good thermal stability, high triplet energy level (E-T) and suitable frontier orbital levels. Green PhOLEDs hosted by CzTrz and BCz2 show turnon voltage (V-on) of 3.5 and 3.8 V, maximum luminance (L-max) of 30,280 and 35,050 cd m(-2), and maximum external quantum efficiency (EQE(max)) of 15.49 and 11.84%, respectively. Remarkably, the CzTrz-based device reveals an extremely low efficiency roll-off at the high luminance, for example, 15.35% at 1000 cd m(-2) and 13.85% at 5000 cd m(-2), corresponding to merely 0.9% and 10.6% roll-off percentage, which is among the best results ever reported as green bipolar hosts.