The Prospects and Challenges for Ambi‐polar Vacancy‐Ordered Double‐Perovskite Cs2SnI6 Toward Realization of High‐Efficiency Air‐Stable Solar‐Cells

The rapid advancements in material research for lead‐free inorganic metal halide perovskites have fueled the pathway to design environmentally benign solar‐cells to cater the energy requirements for future generations. The vacancy‐ordered double‐perovskite Cs 2 SnI 6 with an optimum band‐gap (≈1.3 eV), high absorption coefficient (≈10 5 cm −1 ), ambi‐polar charge carrier transport, and high structural and compositional stability coupled with simple cost‐effective solution‐based synthesis techniques seems to be an excellent candidate to design air‐stable high‐efficiency solar‐cell‐based applications. The review focusses on the structure–property relationship in Cs 2 SnI 6 and its critical dependency on growth precursors, conditions, and methods. The recent advancements in material and additive engineering to obtain phase‐pure uniform and continuous Cs 2 SnI 6 films and myriad methods to modulate its optoelectronic properties are summarized. The nature, origin, and type of charge‐carriers in intrinsic and doped Cs 2 SnI 6 are extensively discussed. The applications of Cs 2 SnI 6 in different solar‐cell configurations are critically reviewed and its recent progress and challenges to achieve the ultimate theoretical Shockley–Queisser limit of 30–33% is presented. The recent experimental findings on the stability and performance of Cs 2 SnI 6 ‐based solar‐cells under ambient and controlled conditions would be discussed to highlight its feasibility for the design and development of air‐stable high‐efficiency solar‐cells.