Comparison of symmetric and asymmetric bipolar type high triplet energy host materials for deep blue phosphorescent organic light-emitting diodes

Symmetric and asymmetric bipolar host materials for deep blue phosphorescent organic light-emitting diodes were developed and the chemical structure of the host materials was correlated with the device performances. The bipolar host with the asymmetric molecular structure was better than the host with symmetric molecular structure in terms of driving voltage and quantum efficiency due to better charge transport properties. A high quantum efficiency of 24.5% and a high power efficiency of 31.0 lm W ^-1 were achieved in the deep blue device using the asymmetric bipolar host due to balanced charge transport and low driving voltage.