An ambipolar phosphine oxide-based host for high power efficiency blue phosphorescent organic light emitting devices

We report blue electrophosphorescent organic light emitting devices with an ambipolar host material, 4-(diphenylphosphoryl)-N,N-diphenylaniline (HM-A1), doped with FIrpic (iridium (III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate). The ambipolar nature of the host was verified using single carrier devices. The power efficiency of devices with PO15 (2,8-bis(diphenylphosphoryl)dibenzothiophene) electron transport layer (ETL) showed optimized performance when the ETL thickness was 500 Å, giving a peak power efficiency of 46 lm/W (corresponding external quantum efficiency (EQE) of 17.1%). The EQE and power efficiency at the brightness of 800 cd/m2 were measured with no light outcoupling enhancement and found to be 15.4% and 26 lm/W, respectively.