Highly efficient blue, orange and red PhOLEDs with low roll-off of efficiency using a carbazole dendritic thermally activated delayed fluorescence (TADF) material as host

Abstract

Numerous efforts have been devoted to improve the device efficiency of phosphorescent organic light-emitting diodes (PhOLEDs), however, strategies to suppress the device efficiency roll-off are still in urgent need. Here, a general and effective approach to boost the efficiency and suppress the efficiency roll-off of PhOLEDs is proposed, that is, utilizing TADF material with high triplet energy (ET) as the host for blue, orange and red phosphorescent dopants is proposed. In this work, we investigate the performance of these PhOLEDs based a new TADF host phenylbis(4-(3,3″,6,6″-tetra-tert-butyl-9′H-[9,3′:6′,9″-tercarbazol]-9′-yl)phenyl)phosphineoxide (TPPOCz). The blue device based on the TPPOCz host exhibit efficiencies of 43.6 cd A−1 and 20.4%, and small efficiency roll-off of 2.1% and 2.9% for CE and EQE from the peak efficiencies to these at 1000 cd m−2. We compared the performances with that reported in literature, and confirmed these devices in this work are among the best of PhOLEDs. These results can be ascribed to the rapid reverse intersystem crossing (RISC) process and high triplet energy (ET). These excellent performances indicating the potential of TADF host for the realization of highly efficient and stable devices in future.