Effect of Residual Chloride in FAPbI₃ Film on Photovoltaic Performance and Stability of Perovskite Solar Cell

Methylammonium chloride (MACl) has been used as an additive in a formamidinium lead iodide (FAPbI₃) precursor solution for high-efficiency perovskite solar cells (PCSs), where the chloride ion is known to have a positive effect on photovoltaic performance. However, we have found that the residual chloride in the perovskite film has an adverse effect on the device stability. Here, we report an improved stability of PSCs by elimination of residual chloride via postheat-treatment (PHT). Removal of the residual MACl on the perovskite grain surface is accompanied by conversion of surface FAPbI₃ to PbI₂. Compared with the control perovskite film, the PHT-induced perovskite film shows a longer charge carrier lifetime, which is responsible for an increase in the reverse scanned power conversion efficiency from 21.17% to 23.20%. Moreover, long-term stability tested under humid air conditions for over 1000 h shows that the chloride-removed perovskite film is much more stable than the control film with residual chloride.