Highly efficient thermally activated delayed fluorescence devices using a phosphorescent dye as host

In this work, we further researched the influence of heavy atom on the electroluminescent (EL) performances of organic light-emitting diodes (OLEDs) containing thermally activated delayed fluorescence (TADF) materials as emitters by utilizing iridium(III)bis(4’,6’-difluorophenylpyridinato)tet-rakis(1-pyrazolyl)borate (Ir(mppy)3) as the host of the assistant light-emitting layer (EML) and 2-[4-(diphenylamino)phenyl]-10,10-dioxide-9H-thioxanthen-9-one (TXO-TPA) as emitter. Though optimizing the doping concentration of TXO-TPA and the thickness of assistant EML, we have successfully improved the EL performances of TXO-TPA based device by analyzing energy transfer, exciton quenching progresses and carrier distribution within EMLs. Finally, the optimal device obtained high current efficiency and external quantum efficiency of 38.92 cd/A and 12.41% at 2000 cd/m2 (3.2 V). Meanwhile, the optimal device has a slower efficiency roll-off with maximum current efficiency of 42.43 cd/A (EQE=12.95%) with a long LT50 (the time for brightness decay to 50% of the initial brightness) lifetime of 6700 h at 2000 cd/m2.