Simple Bipolar Hosts with High Glass Transition Temperatures Based on 1,8-Disubstituted Carbazole for Efficient Blue and Green Electrophosphorescent Devices with Ideal Turn-on Voltage

Two hybrids based on 1,8-disubstituted carbazole, 1,8-OXDCz and 1,8-mBICz, have been designed and synthesized through a facile process. The incorporation of oxadiazole or N-phenylbenzimidazole moieties at the 1,8-positions of carbazole greatly improves its morphological stability, giving glass transition temperatures (Tg) as high as 138 and 154 degrees C, respectively. Blue phosphorescent organic light-emitting devices (PhOLEDs) with 1,8-mBICz exhibit almost the same performance as a similarly structured device based on the mCP host, and green PhOLEDs employing the new host material 1,8-OXDCz exhibit an ideal turn-on voltage (2.5 V at 1.58 cdm-2), a maximum current efficiency (eta c,max) of 73.9 cdA-1, and a power efficiency (eta p,max) of 89.7 lmW-1. These results are among the best performances of [Ir(ppy)3]-based devices with simple device configurations.