Stability Improvement of Tin‐Based Halide Perovskite by Precursor‐Solution Regulation with Dual‐Functional Reagents

Abstract Tin‐based halide perovskites have attracted great attention in the perovskite solar cells (PSCs) community with their suitable band gaps, excellent optoelectronic properties, and non‐toxicity. However, because of their poor chemical stability, it is challenging to fabricate highly stable and efficient tin PSCs (TPSCs). In this study, the origin of the Sn 2+ oxidation ahead of film formation is concentrated on, and it is found that the ionization of SnI 2 in precursor plays a decisive role. Accordingly, SnI 2 dissociation and the subsequent Sn 2+ oxidation can be restricted in precursor by employing reductive complexes as additives. This dual‐functional source‐regulating strategy effectively helps prepare high‐quality perovskite films with low Sn 4+ defect densities. As a result, the unencapsulated TPSCs show a considerable power‐conversion efficiency of 10.03% (certified 9.38%) and maintain 90% of its initial efficiency after 1000 h of light aging testing.