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.