High efficiency thermally activated delayed fluorescent devices using a mixed host of carbazole and phosphine oxide derived host materials

• High efficiency green thermally activated delayed fluorescent device using a mixed host.
• Mixed host of carbazole and diphenylphosphine oxide derived host materials.
• Efficient energy transfer from the mixed host to thermally activated delayed fluorescent dopant.

A mixed host of a carbazole type host and phosphine oxide type host materials was developed and used as the host for green thermally activated delayed fluorescent (TADF) device to obtain high quantum efficiency and to manage the emission color of the TADF device. Two mixed hosts, 1,3-bis(N-carbazolyl) benzene (mCP):diphenylphosphine oxide-4-(triphenylsilyl) phenyl (TSPO1) and mCP:9,9-spirobifluoren-2-yl-diphenylphosphine oxide (SPPO1) were used as the mixed hosts and the device characteristics of the mixed host devices were investigated. The electron transport type of the mixed host devices could manage the quantum efficiency and emission color of the TADF devices. High quantum efficiency of 27.5% was achieved in the green TADF OLEDs using the mixed host of mCP:TSPO1 and the emission peak wavelength could be shifted by more than 10 nm without sacrificing the quantum efficiency of the TADF devices.