Bipolar Fluorenylcarbazole-based Host Materials for Efficient Red Phosphorescent Organic Light-emitting Diodes

Achieving high-efficiency red phosphorescent organic light-emitting diodes(PhOLEDs) is still a challenge, which is largely related to the host material used in device fabrication. Two new bipolar hosts, 2-(9H-carbazol-9-yl)-7, 7-dimethyl-5-(4-phenylquinazolin-2-yl)-5, 7-dihydroindeno[2, 1-b]carbazole(FC-CZ-PQZ) and 2-(4-(9H-carbazol-9-yl)phenyl)-7, 7-dimethyl-5-(4-phenylquinazolin-2-yl)-5, 7-dihydroindeno[2, 1-b]carbazole(FC-BCz-PQZ), were designed and synthesised as host materials to fabricate red PhOLEDs. The two compounds exhibited excellent physical properties with high thermal stabilities and balanced charge transport. FC-BCz-PQZ has a better bipolar carrier transport compared to FC-CZ-PQZ. FC-BCz-PQZ-based device demonstrated good electroluminescence performance with the maximum current efficiency, power efficiency and external quantum efficiency of 13.5 cd/A, 14.2 lm/W and 14.8%, respectively, suggesting its promising application as a host material for red PhOLEDs.