Methylammonium and Bromide-Free Tin-Based Low Bandgap Perovskite Solar Cells

Lead halide-based perovskite solar cells (PSCs) are intriguing candidates for photovoltaic technology because of their high efficiency, low cost, and simple process advantages. Owing to lead toxicity, PSCs based on partially/fully substituted Pb with tin have attracted tremendous attention, which would enable the ideal bandgap to approach the Shockley-Queisser (S-Q) limit. Especially, methylammonium (MA), bromide-free, tin-based perovskites are striking, because of the intrinsic poor stability of MA and blue shift caused by the incorporation of Br-. The first section of this review emphasizes the motivation for studying single-junction MA, Br-free, and Sn-based perovskites. The film quality improvement strategies of Sn-based perovskites, including additive, composition, dimensional, and interface engineering toward high-efficiency devices are comprehensively overviewed. Moreover, strategies to improve stability, where shelf, thermal and operational stabilities of the devices are summarized. Finally, this review concludes with a discussion of actual limitations and future prospects for Sn-based PSCs.