Unraveling Ion Migration Mechanisms under Operating Conditions in Perovskite Solar Cells by Variable-Load Transient Photoelectric Technique

Ion migration in perovskite solar cells (PSCs) significantly impacts their photoelectric performance and physicochemical stability. Existing research has predominantly focused on inhibiting ion migration through chemical strategies or observing it under open-circuit or short-circuit conditions. This focus has led to a limited theoretical understanding and control of ion migration under practical conditions, constraining advances in long-term stability. In this study, we introduce a novel variable-load transient photoelectric technique (VL-TPT) to investigate ion migration dynamics in PSCs under practical operating conditions. Results show that ion accumulation correlates with photogenerated carrier concentration under open-circuit conditions. During operation, ion accumulation decreases with reduced load, because charge is transferred to the external circuit, leading to a reduction in carrier concentration within the device. An unusual increase in interface ions is observed at low loads due to interactions between charges accumulated in the potential well and ions. Introducing FA⁺ in MA_0.75FA_0.25PbI₃ devices suppresses ion migration in the open-circuit state but accelerates interface ion buildup under operating conditions. These findings provide valuable insights for enhancing device stability and performance.