In recent years, inorganic CsPbBr3-based perovskites have accomplished considerable progress owing to their superior stability under harsh humid environment.

Since the booming research on perovskite solar cells (PSCs), organic–inorganic hybrid halide perovskites have triggered widespread research attention. This is seen in the unprecedented improvement of the power conversion efficiency (PCE) from an initial 3.8% to a remarkable 25.5%. Despite the fascinating improvement in PCEs, the toxicity of the detrimental lead element is a major limiting factor that hampers the commercialization prospect of lead‐based materials. Extensive efforts have been dedicated to the progress of lead‐free, stable, and ecofriendly perovskite materials for green‐energy applications. Recently, double‐halide Cs2SnI6 perovskite emerged as a star material due to its favorable optoelectronic properties, stable nature, and environmental friendliness. Thus, an in‐time review to recapitulate the recent advances of Cs2SnI6 is critical to provide viable theoretical and experimental strategies for synergic optimization of perovskite films. Herein, the theoretical and experimental understandings of the properties of Cs2SnI6 are summarized and the different fabrication methodologies and their influences on the properties of Cs2SnI6 are discussed. The application potential of Cs2SnI6 is further reviewed and the limiting factors that influence the performance of Cs2SnI6 devices are highlighted. In the end, prospective research directions to improve the optoelectronic properties are presented for developing efficient Cs2SnI6 devices.

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Summary Cs2SnI6 has recently been reported as a promising material to replace Pb‐based perovskite materials due to its appropriate optical and electrical properties as well as high stability in the ambient environment. Here, the study focuses on introducing different types of reactants to form highly stable Cs2SnI6 films via a modified two‐step process. The structural analysis was examined using the X‐ray diffraction measurements and lattice strain and average crystallite size were calculated by the Williamson hall method. All the prepared films showed excellent phase stability at 210°C with no major CsI impurity peak. Adding excess I2 with SnI4 at 225°C resulted in inhibiting the decomposition of the film. Raman measurements revealed the presence of three first‐order modes at 78, 92, 126 cm−1, and a higher mode at 248 cm−1, respectively. The UV‐vis results confirm the direct semiconductor nature of Cs2SnI6 with bandgap ranging from 1.31‐1.37 eV. The iodine‐rich preparation of the films resulted in improved photoluminescence and high hole mobility of 329 (cm2V−1 s−1). The present work will provide useful guidance in the preparation protocol of Cs2SnI6 perovskite solar cells.

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