Benzimidazole-triazine based n-type hosts with twisted structure and high triplet energy level for efficient blue narrowband emitting OLEDs

Two benzimidazole-triazine based n-type hosts with twisted structure namely BIZ-2Me-TRZ and BIZ-6Me-TRZ were designed by combining two electron-transporting fragments of 1-phenyl-1H-benzo[d]imidazole and diphenyltriazine with a unit of 2 ' or 6 ' - position methyl substituted phenyl to achieve high triplet energy level over 3.0 eV. The BIZ-6Me-TRZ exhibits high electron mobility up to 1.27 x 10-4 cm2 V-1 s- 1, which is two orders of magnitude higher than that of BIZ-2Me-TRZ (8.11 x 10-6 cm2 V-1 s-1), due to its moderate dihedral angle between the phenyl linker and triazine. The blue narrowband emitting device using BIZ-6Me-TRZ as the host shows low turn-on voltage of 2.8 V and high external quantum efficiency (EQE) of 29.2%. The device EQE could be further enhanced to 32.7% by using the n-type BIZ-6Me-TRZ as the acceptor to form exciplex host with a p-type material for improving the exciton utilization efficiency.