Recent progress of host materials for highly efficient blue phosphorescent OLEDs

Phosphorescent organic light-emitting diodes (PHOLEDs) show a bright future for flat-panel displays and solidstate lighting due to higher quantum efficiencies compared with traditional fluorescent OLEDs. This review focuses on small-molecular organic host materials for blue PHOLEDs with external quantum efficiency higher than 20%. Hole transport-type, electron transport-type and bipolar transport hosts are introduced according to their charge transporting properties. Their molecular structures and physical properties such as triplet energy, HOMO/LUMO energy levels and thermal stabilities, as well as device performances of host materials for blue and deep-blue PHOLEDs are comprehensively demonstrated. It is expected to provide reference value for the exploitation of new organic host materials and the commercialization of OLEDs.