Confinement of charge carriers and excitons in electrophosphorescent devices: Mechanism of light emission and degradation

Abstract

Charge-carrier and exciton confinement is essential for efficiency and stability enhancment of electrophosphorescent devices. Emission-layer lifetimes of a 4,4'-N,N'-dicarbazole-biphenyl host doped with either a red- or green-emitting dye (upper and lower figures) show a strong dependence and near independence, respectively, on the type of exciton blocking layer used (four are shown). This is explained using energy-level differences and corresponding charge-trapping behavior.