Current-Density Dependence of Transient Properties in Green Phosphorescent Organic Light-Emitting Diodes

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The current-density dependence of the transient characteristics of a green phosphorescent organic light-emitting diode (OLED) with tris(2-phenylpyridine)iridium(III) [Ir(ppy)3] as the emissive layer and the quenching process, which contributes to roll-off in a device, were investigated. A maximum quantum efficiency of 11% and luminance of 45,000 cd/m2 were achieved for a green OLED. The behaviors of the transient characteristics and efficiency 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 cut-off frequency of the device is mainly limited by the phosphorescent recombination lifetime.
2011-04-25