Chloride Engineering for Boosting Perovskite Photovoltaics: Impact on Precursor Coordination, Crystallization, and Film Quality

Abstract Perovskite solar cells (PSCs) have seen rapid advancements over the past decade, driven by their exceptional optoelectronic properties and high power conversion efficiencies. Cl‐based additives strategy has significantly contributed to these advancements by enhancing crystallinity, improving preferred orientation, and optimizing the surface morphology of perovskite films. This review provides a comprehensive summary of recent advancements and insights into the critical role of Cl‐based additives in perovskite photovoltaics, focusing on the mechanisms behind Cl incorporation and its effects on film and device performance. First, the impact of Cl on precursor solution coordination and colloidal characteristics is discussed. Then, how Cl‐based additives influence the phase transitions of perovskites, including methylammonium lead iodide (MAPbI 3 ), formamidinium lead iodide (FAPbI 3 ), and 2D perovskites is examined. Furthermore, the impact of Cl‐based interfacial treatments on perovskite film quality is explored. Based on these insights, the overall impact of Cl treatments is also reviewed on the properties of perovskite films. Finally, a brief overview of the remaining challenges and future perspectives are provided to guide ongoing research efforts toward optimizing Cl additive engineering for high‐performance PSCs.