Analysis of efficiency characteristics of green phosphorescent organic light-emitting devices

Efficiency characteristics of green phosphorescent organic light-emitting devices (PHOLEDs) with different host materials and device structures were investigated by examining the luminance efficiency-current density curves and electroluminescence spectra. The efficiency of PHOLEDs at low current density as well as at high current density was greatly affected by energy levels and carrier transport properties of the host and hole/electron transporting materials. The devices exhibited high initial luminance efficiency when hole-electron recombination was well confined in the emitting layer (EML). Efficiency roll off with increasing current density was observed as hole-electron recombination and charge balance in EML deteriorated with current density.