Performance Boost by Dark Electro Treatment in MACl-Added FAPbI₃ Perovskite Solar Cells

Halide anion migration in organic–inorganic metal halide perovskites significantly influences the power conversion efficiency (PCE) and hysteresis of perovskite solar cells (PSCs). These materials are sensitive to various external stimuli such as light, heat, and electrical bias, highlighting the need for novel post-manufacturing treatment methods alongside a deeper understanding of their mechanisms. Here, a dark electro (DE) treatment is introduced that applies a negative-positive-negative bias to PSC under dark conditions, which is particularly effective for formamidinium (FA) lead iodide (FAPbI3) PSCs processed with a methylammonium chloride (MACl) additive. The DE treatment, followed by light soaking, results in an average PCE increase of 2.9 ± 1.8% (from an initial 18.2 ± 2.0% to 21.1 ± 0.8% after treatment) with a notable decrease in deviation. It is discovered that residual chloride anions from MACl play a critical role in the DE treatment. The migration of halide anions under a shaking electric bias is investigated using energy-dispersive X-ray spectroscopy (EDX) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). This study elucidates the distribution and impact of residual chloride anions, providing insights into the mechanisms underlying the DE treatment.