Improved High-Brightness Efficiency of Phosphorescent Organic LEDs Comprising Emitter Molecules with Small Permanent Dipole Moments

Weaker triplet-triplet annihilation (TTA) is observed in organic solid mixed systems comprising the phosphorescent emitter Ir(ppy)(2)(acac), which has a smaller dipole moment than the reference compound Ir(ppy)(3). Spectral and time-resolved analysis show that the weaker TTA can be explained by lower emitter aggregation, which reduces diffusion-based TTA.