Energy Barriers Restrict Charge Carrier Motion in MAPI Perovskite Films

Understanding of charge trapping processes in halide perovskites is vital to further improve performance of perovskite optoelectronic devices such as solar cells, photodetectors, and LEDs. In this work, transient photocurrent, time-delayed collection field and transient fluorescence techniques along with numerical simulations are combined to address charge carrier trapping processes during their lateral motion in prototypical methylammonium lead iodide perovskite films formed on interdigitated electrodes. Carrier mobility decreases on hundreds of ns timescale, and its rate depends on the motion character-it is faster when charge carriers drift in the electric field and slower when the motion is caused by diffusion only. This difference becomes particularly evident at low temperatures. Based on the time-delayed collection field data and carrier motion modelling results, it is demonstrated that the rapid mobility decay at low temperatures is mainly caused by the energy barriers, most likely formed at crystallite boundaries. Even though these barriers are surmountable at room temperature, they still play a major role in determining carrier mobility and diffusion rates. Suggested concept of the potential barriers moves beyond the conventional understanding of carrier mobility, diffusion, and recombination processes in hybrid perovskites.