Novel bipolar host materials based on 1,3,5-triazine derivatives for highly efficient phosphorescent OLEDs with extremely low efficiency roll-off

Recently, bipolar host materials have attracted considerable attention because they can achieve balanced charge injection/transport in phosphorescent organic light emitting diodes (PhOLEDs) and consequently obtain excellent device performance. In this work, two bipolar host materials, namely, 3-(4,6-diphenyl-1,3,5-triazin-2-yl)-9-phenyl-9H-carbazole (DPTPCz) and 3-(4,6-diphenoxy-1,3,5-triazin-2-yl)-9-phenyl-9H-carbazole (DPOTPCz), have been designed, synthesized and characterized. With high triplet energy levels of 2.78 and 2.86 eV for DPTPCz and DPOTPCz, respectively, two compounds are considered promising bipolar host materials for PhOLEDs. Blue and green PhOLEDs based on these two new compounds show excellent performances. The phosphorescent devices based on DPTPCz exhibit maximum external quantum efficiencies of 14.4% (for blue device) and 21.2% (for green device), and maintain high efficiencies of 11.9% and 20.0% even at a high luminance of 10 000 cd m(-2).