A-Site Cation Engineering of Metal Halide Perovskites: Version 3.0 of Efficient Tin-Based Lead-Free Perovskite Solar Cells

Pb-based metal halide perovskites (MHPs) have emerged as efficient light absorbers in third-generation photovoltaic devices, and the latest certified power conversion efficiency (PCE) of Pb-based perovskite solar cells (PSCs) has reached 25.2%. Despite great progress, Pb-based MHPs are affected by toxicity, which hinders their market entry in a potential future large-scale commercialization effort. Therefore, the exploration of Pb-free MHPs has become one of the alternative solutions sought in the community. Among all the Pb-free MHPs, Sn-based MHPs show great promise owing to their similar or even superior theoretical optoelectronic characteristics. After several years of development, the PCE of Sn-based PSCs has recently been approaching 10%, with the breakthroughs mainly coming from A-site cation engineering of Sn-based MHPs. In this review, the crucial status of A-site cation engineering strategies in the research of Sn-based PSCs is highlighted. First, the way the features of A-site cation influence the structure and characteristics of MHPs is systematically demonstrated. Then, the state-of-the-art developments, focusing on A-site cation engineering of Sn-based MHPs, are comprehensively reviewed. Subsequently, the current challenges and opportunities for further boosting the performance of Sn-based PSCs are discussed. Finally, conclusions and perspectives on the promising Sn-based optoelectronic devices are discussed.