Triazine-dibenzocarbazole based bipolar host materials for highly luminescent green and yellow phosphorescent organic light emitting diodes

Two new bipolar host materials, 7-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-7H-dibenzo[a,g]carbazole (TRZ-DBC1) and 7-(4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-7H-dibenzo[a,i]carbazole (TRZ-DBC2) were designed and synthesized between dibenzocarbazole donor and triazine acceptor. The both materials revealed excellent thermal stabilities and good bipolar characteristics. We have fabricated yellow and green phosphorescent OLED devices to study the host performances. The TRZ-DBC1 based yellow device showed excellent current efficiency of 71.4 cd/A, while CBP based reference device showed lower efficiency of 58.0 cd/A. The external quantum efficiency of TRZ-DBC1 (25.4%) and TRZ-DBC2 (22.4%) were outstanding when compare to reference device (19.1%). The TRZ-DBC2 used as host material for green phosphorescent OLED due to its higher triplet energy of 2.71 eV. The green phosphorescent OLED exhibited excellent current efficiency of 75.9 cd/A, and excellent external quantum efficiency of 24.7%. These two bipolar host materials would be promising candidates for green and yellow phosphorescent OLEDs for display application.