Accurate and fast master equation modeling of triplet-triplet annihilation in organic phosphorescent emission layers including correlations

Triplet-triplet annihilation (TTA) in phosphorescent emission layers of modern organic light-emitting diodes
compromises their performance and device lifetime. TTA can occur by a Förster-type interaction between two
triplets, leading to a loss of one of them. The TTA process gives rise to correlations in the positions of the
surviving triplets, which complicate its study. These correlations can in principle be accounted for exactly in
kinetic Monte Carlo (KMC) simulations, but such simulations are computationally expensive. Here, we present
master equation modeling of TTA that accounts for correlations in a computationally efficient way. Cases without
and with triplet diffusion, which partly washes out correlations, are considered. We calculate the influence of
TTA on transient photoluminescence experiments, where it leads to a deviation from exponential decay, and on
steady-state emission efficiency. A comparison with KMC simulations shows that our master equation modeling
is an accurate and computationally competitive alternative.