Carbazole-benzonitrile derivatives as universal hosts for triplet-harvesting blue organic light-emitting diodes

In this study, we proposed two carbazole-benzonitrile-based bipolar hosts, namely 2,6-bis(3-(9H-carbazol-9-yl)phenoxy)benzonitrile (3-CzPB) and 2,6-bis(4-(9H-carbazol-9-yl)phenoxy)benzonitrile (4-CzPB), for improving the efficiency of blue phosphorescent organic light-emitting diodes (PhOLEDs) by connecting the carbazole donor and benzonitrile acceptor at the 3- and 4-positions, respectively, of the phenoxy linker. The efficient hole and electron transport properties revealed that the two hosts exhibit effective bipolar host characteristics. Therefore, blue PhOLEDs using the 3-CzPB host achieved a high external quantum efficiency of 26.1% and 26.0% in sky-blue and deep-blue devices, respectively. Furthermore, 3-CzPB-hosted blue thermally activated delayed fluorescence (TADF) and multi-resonance TADF devices achieved a high external quantum efficiency of 26.8% and 31.1%, respectively. This result demonstrated that the 3-CzPB host can be used as a universal host for triplet exciton harvesting blue organic light-emitting diodes.