Highly efficient blue organic light-emitting devices based on an exciplex host with thermally activated delayed fluorescence

Thermally activated delayed fluorescence (TADF) resulting from the harvesting of triplet excitons has currently emerged as an excellent candidate for enhancing the efficiency of organic light-emitting devices (OLEDs). Highly efficient blue OLEDs based on an exciplex host with carbazole/thioxanthene-S, S-dioxide (EBCz-ThX) and 2-phenyl-bis-4, 6-(3, 5-di-4-pyridylphenyl) pyrimidine (B4PYPPM) acting as a blue TADF emitter were fabricated. The maximum values of the current and the power efficiency for the blue OLEDs with an EBCz-ThX:B4PYPPM exciplex host were 22.46 cd/A and 28.23 lm/W, respectively. The power efficiency of blue OLEDs with an exciplex host was much higher than that of conventional blue OLEDs. The efficiency enhancement of the blue OLEDs based on an exciplex system with a TADF emitter was attributed to the efficient up-conversion of the triplet excitons in the EBCz-thx:B4PYPPM and to the efficient energy transfer from the exciplex host to the blue TADF emitter.