Strategies toward Suppression of Sn(II) Oxidation for Stable Sn–Pb Perovskite Solar Cells

For the increasing demand for renewable energy to reduce carbon dioxide emissions, a high-efficiency, low-cost perovskite solar cell (PSC) is one of the most promising technologies. To further improve the power conversion efficiency, a tandem device comprising a bottom cell with low band gap perovskite is a potential candidate. Tin–lead alloyed perovskite is suitable for this purpose due to its low band gap of about ∼1.2–1.3 eV. However, the stability of Sn(II) in the alloyed perovskite films poses a significant challenge to the progress of the technology. Here, we identify the origin of tin instability in tin–lead perovskite and analyze the promising stability improvement strategies available in the literature. In addition, we offer a perspective for further development of strategies to enhance the stability of the material and the device's performance.