A model based on defect generation by exciton‐polaron annihilation interactions between the emitter and host molecules, in a blue phosphorescent OLED, is shown to fit well with experimental data. A blue PHOLED with (0.15, 0.25) chromaticity is shown to have a half‐life, from 1,000 nits, of 690 hrs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92134/1/1.3069766.pd