How molecular aggregation affects internal quantum efficiency in organic phosphorescent light-emitting diodes

We investigate whether typical host–guest phosphorescent organic light-emitting diodes are at an intrinsic efficiency limit due to the long-range nature of the bimolecular loss mechanism in these devices. Using kinetic Monte Carlo simulations and developing models that can mimic realistic and ideal distributions of emitter molecules, we discuss how the interplay among exciton relaxation, transport, and annihilation is affected by the prevalent molecular aggregation in state-of-the-art emission layers. Regarding the internal quantum efficiency, we find a potential increase of ∼15% (and a minimum relative increase of 20%) for devices with suppressed aggregate formation. We also discuss conditions under which the system reaches its inherent limitation of efficiency.