Lithium Fluoride Assisted Preparation of High‐Performance All‐Inorganic CsPbI3 Perovskite Solar Cells

All‐inorganic CsPbI 3 perovskite is an ideal solar material with an appropriate bandgap (≈1.73 eV) that can be used for the top cell in tandem cells matched to crystalline silicon or low‐bandgap perovskites. Efficient all‐inorganic perovskite solar cells (PSCs) provide the cornerstone for efficient tandem cells. However, all‐inorganic PSCs are less efficient than organic–inorganic hybrids PSCs, and because CsPbI 3 is incompatible with water, the stability of perovskite must be improved. Herein, a novel method for preparing efficient and stable PSCs via ionic chemical doping is proposed. Lithium fluoride as an inorganic ionic dopant can control grain growth and get larger grain sizes. The crystal structure, morphology, and electrochemical impedance spectroscopy of LiF‐doped all‐inorganic perovskite films are studied to determine the relationship between film quality and device performance. The doping of 2 mol% LiF considerably enhances the performance of the device, eliminates the hysteresis effect of the device, and the maximum power conversion efficiency of PSCs is raised to 17.02%. Additionally, device stability is greatly enhanced.