Highly efficient deep blue phosphorescent organic light-emitting diodes are developed using novel phenylcarbazole-based phosphine oxide host materials (PPO1 and PPO2). A deep blue phosphorescent dopant, tris((3,5- difluoro-4-cyanophenyl)pyridine) iridium, is doped into PPO1 and PPO2 at a doping concentration of 15% and a high quantum efficiency of 18.4% is obtained with color coordinates of (0.14, 0.15).