Elucidating the Recombination and Annihilation Rates in Blue Thermally Activated Delayed Fluorescence Emitter‐Based OLEDs Using Transient Measurements

Abstract The recombination rate and the exciton annihilation rates are crucial for understanding the exciton dynamics in organic light‐emitting diodes (OLEDs). In this work, the recombination rate is determined from the relative carrier mobility estimated using a time‐correlated single photon counting‐based transient electroluminescence measurement. The estimation of the recombination rate from the carrier mobility for the thermally activated delayed fluorescence (TADF) emitter dimethyl‐9,10‐dihydropyridine‐diphenyl sulphone (DMAC‐DPS) and its blends helps to understand the effect of the host and dopants. The pristine devices show an enhanced recombination rate compared to the blended device, due to the high‐field dependence factor estimated from the Poole–Frenkel behavior. Furthermore, the exciton–exciton annihilation rates in both systems are quantified using a kinetic model for optical excitation employing a global optimization method based on a genetic algorithm. The results indicate that in the blended DMAC‐DPS system, the exciton–exciton annihilations are significantly reduced in comparison to the pristine system. Comparison of pristine and blended systems reveals the host–guest interactions governing recombination dynamics and exciton losses in practical OLEDs.