Present Status and Research Prospects of Tin‐based Perovskite Solar Cells

Sn‐based halide perovskites have attracted much interest due to their highly valuable electrical and optical properties. The promising optical and electrical properties of Sn‐based perovskites have enticed a lot of research to focus on developing the strategies and explore the in‐depth material characteristics. Sn‐halide perovskites exhibit apparent merits and demerits. The ideal electrical and optical properties are even better than that of Pb‐analogs, namely close‐to‐optimal bandgap, strong optical absorption, and good carrier mobilities. However, the present achievement of Sn‐halide perovskite solar cells is not satisfactory, which is commonly attributed to relatively low defect tolerance, fast crystallization, and oxidative instability. The efficiency of Sn‐based perovskites is far ahead, with a 9% power conversion efficiency (PCE), than the other (Ge, Bi, Sb, Cu, etc.) Pb‐free options but simultaneously lagging far behind Pb‐based analogs that have a 25.2% PCE. This review is aimed at presenting milestone works and revealing the pros and cons of Sn‐halide perovskites. In addition, the defect physics of Sn‐based perovskites is described. The improvement of open‐circuit voltage is a critical issue for Sn‐halide perovskites to compete with Pb‐based perovskites. The understanding of defect physics plays an instrumental role in designing strategies for efficient and robust Sn‐halide perovskite solar cells. This review presents the present status and the future perspectives of Sn‐based perovskite solar cells. The strategies to find the breakthrough of highly efficient and robust Sn‐perovskite solar cells are discussed by focusing on current fabrication processes and defect physics scenario including compositional and dimensional engineering.