DACT-II is a bipolar TADF green emitter with electron deficient diphenyltriazine and electron rich 3,6-diphenylaminocarbazole units, joined by a phenyl π linker. Comparing with the parent structure of Cab-Ph-Trz which serves as phosphorescent host material for green and red OLEDs, DACT-II is more electron rich with two extra set of biphenylamines on the 3,6-positions of carbazole.
DACT-II-based OLEDs exhibit a maximum EQE of 29.6% in the absence of out-coupling treatment, indicating an internal quantum efficiency (IQE) of ~ 100%, owing to its S1 and T1 excitons being rapidly converted to photons because of its large oscillator strength and small ΔEST lower than the thermal energy at room temperature. The optimized TADF-OLED device with DACT-II as the emitter and CBP:B4PyMPM as the exciplex host demonstrated an external quantum efficiency (EQE) of 31.7%, with an ultrahigh power efficiency of 145.5 lm W-1 and an unprecedented low turn-on voltage of 2.22 V.