Stable Lead‐Free Tin Halide Perovskite with Operational Stability >1200 h by Suppressing Tin(II) Oxidation

Sn-based perovskites are the most promising alternative materials for Pb-based perovskites to address the toxicity problem of lead. However, the development of Sn^II -based perovskites has been hindered by their extreme instability. Here, we synthesized efficient and stable lead-free Cs₄ SnBr₆ perovskite by using SnF₂ as tin source instead of easily oxidized SnBr₂ . The SnF₂ configures a fluorine-rich environment, which can not only suppress the oxidation of Sn²⁺ in the synthesis, but also construct chemically stable Sn-F coordination to hinder the electron transfer from Sn²⁺ to oxygen within the long-term operation process. The SnF₂ -derived Cs₄ SnBr₆ perovskite shows a high photoluminescence quantum yield of 62.8 %, and excellent stability against oxygen, moisture, and light radiation for 1200 h, representing one of the most stable lead-free perovskites. The results pave a new pathway to enhance the optical properties and stability of lead-free perovskite for high-performance light emitters.