Stabilized Wide Bandgap Perovskite Solar Cells by Tin Substitution

Wide bandgap MAPb(I_1-yBr_y)₃ perovskites show promising potential for application in tandem solar cells. However, unstable photovoltaic performance caused by phase segregation has been observed under illumination when y is above 0.2. Herein, we successfully demonstrate stabilization of the I/Br phase by partially replacing Pb²⁺ with Sn²⁺ and verify this stabilization with X-ray diffractometry and transient absorption spectroscopy. The resulting MAPb_0.75Sn_0.25(I_1-yBr_y)₃ perovskite solar cells show stable photovoltaic performance under continuous illumination. Among these cells, the one based on MAPb_0.75Sn_0.25(I_0.4Br_0.6)₃ perovskite shows the highest efficiency of 12.59% with a bandgap of 1.73 eV, which make it a promising wide bandgap candidate for application in tandem solar cells. The engineering of internal bonding environment by partial Sn substitution is believed to be the main reason for making MAPb_0.75Sn_0.25(I_1-yBr_y)₃ perovskite less vulnerable to phase segregation during the photostriction under illumination. Therefore, this study establishes composition engineering of the metal site as a promising strategy to impart phase stability in hybrid perovskites under illumination.