Effects of mixed host spatial distribution on the efficiency of blue phosphorescent organic light-emitting diodes

We present a systematic study of how graded-host profile in the emissive layer (EML) affects the efficiency of blue phosphorescent organic light-emitting diodes. Three sets of devices with uniformly mixed and linearly graded mixed (LGM) hosts are fabricated with iridium-(III)-bis(4,6-difluorophenyl-pyridinato- N,C2) picolinate as dopant. By varying the position of the dopant within the emissive layer, we show that the LGM architecture improves device efficiency by moving the recombination zone further from the interface thereby reducing quenching due to interactions with charges in the transport layers. © 2012 American Institute of Physics