ABSTRACTThe transient electroluminescence (EL) of phosphorescent organic
light-emitting diodes (OLEDs) was investigated. The behaviors of the
transient characteristics are analyzed using the triplet-triplet
annihilation model. The device exhibited a gradual decrease in quantum
current efficiency owing to the triplet-triplet annihilation at a high
current density. At a higher current density, the reduced rise and decay
times are due to high-density triplet excitons related to the enhanced
triplet-triplet annihilation and the increase of the nonradiative process.
The modulation speed of the devices is mainly limited by the phosphorescent
recombination lifetime.