In Situ Impurity Phase Repair Strategy Enables Highly‐Efficient Perovskite Solar Cells with Periodic Photovoltaic Performance

Abstract The photoactive α‐phase of formamidinium lead iodide perovskite (α‐FAPbI 3 ) is regarded as one of the ideal materials for high‐efficiency perovskite solar cells (PSCs) due to its superior optoelectronic properties. However, during the deposition of α‐FAPbI 3 perovskite films, the presence of impurity phases, such as PbI 2 and δ‐FAPbI 3 , can cause the formation of inherent defects, which leads to suboptimal charge transport and extraction properties, as well as inadequate long‐term stability in the film's morphology and structure. To address these issues, an impurity phase repair strategy is employed using FAI/MASCN mixed vapors to convert the impurity phases into light‐absorbing α‐FAPbI 3 . Meanwhile, this recrystallization process also facilitates the recovery of its characteristic morphology, thereby improving efficiency and enhancing the durability of PSCs. This approach promotes the PSCs to obtain an efficiency of 26.05% (with a certified efficiency of 25.67%, and steady‐state PCE of 25.41%). Additionally, this approach is suitable for the fabrication of large‐area devices, obtaining a 1 cm 2 device with a PCE of 24.52% and a mini‐module (with an area of 17.1 cm 2 ) with a PCE of 22.35%. Furthermore, it is found that this strategy enables cyclic repair of aged perovskite films, with the perovskite solar cells retaining ≈ 94.3% of their initial efficiency after two cycles of repair, significantly enhancing the lifetime of the perovskite solar cells.