Tin halide lead‐free perovskite solar cells (TPSCs) have received tremendous research interest recently due to their nearly ideal bandgap, broad light absorption, non‐toxicity, and environmental friendliness. However, the uncontrollable crystallization process and the facile oxidation of Sn2+ limit the further increase of power conversion efficiency (PCE). To solve these problems, a series of acetates are introduced into the perovskite precursor solution to regulate the crystallization process. It is revealed that formamidine acetate (FAAc) has strong COSn coordination with Sn2+ compared with acetic acid (HAc) and methylammonium acetate (MAAc), which can stabilize the lattice structure, minimize defect states and suppress the oxidation of Sn2+. Meanwhile, benefiting from this coordination ability, it not only leads to large‐size colloidal clusters in precursor but also slows down the crystallization process and improves the crystallinity of tin halide perovskite films. The device with FAAc achieved an increased PCE from initially 9.84% to 12.43%, and it could maintain 94% of its initial value for 2000 h in N2 atmosphere. This work provides a feasible strategy for depositing high‐quality tin perovskite films with low defect density and lattice distortion, which will be crucial for related photovoltaics and other optoelectronic devices.

Tin halide perovskite solar cells (TPSCs) have attracted aggressive research interest in the emerging perovskite photovoltaic devices due to their eco-friendliness as compared to their lead halide counterparts. However, the easy Sn(II)/Sn(IV) oxidation of tin perovskites is a serious impediment to the development of TPSCs. Therefore, a clear understanding of the mechanisms, origins, and effects of the oxidation is essential to further boost the performance and stability of TPSCs. Herein, a systematic overview of the physicochemical process for the Sn(II)/Sn(IV) oxidation in TPSCs from the starting precursors to the final devices is presented. In addition, the effects of oxidation on the performance of TPSCs are then reviewed from crystal structure, defect chemistry, and optoelectronic properties. More importantly, the key issues to suppress the Sn(II)/Sn(IV) oxidation are seriously discussed on the basis of the reported antioxidation strategies. Finally, the challenges and outlooks toward TPSCs with higher power conversion efficiency and stability are proposed.

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