Analysis of Electronic Properties of FAPb1-XSnxI3 Perovskites

Pb-based hybrid organic-inorganic perovskites, such as MAPbI₃ and FAPbI₃, are among the most promising materials to be widely used for light absorption in solar cells. However, Pb-based materials pose safety hazards and cannot be tuned for use as rear cell absorbers in tandem solar cells. Completely substituting Pb with Sn allows lowering the band gap, but also undermines the stability of the materials. In this study, the effects of alloying FAPbI₃ with Sn in place of Pb at different ratios are examined in terms of the band structure, density of states, and charge density, using density functional theory (DFT) methods. It was found that substituting Pb with Sn does not significantly change the structure or dimensions of FAPbI₃, and it generally lowers the band gap. The band gap is lowered due to the contribution of Sn to the conduction band minimum of the material. Due to the band gap tunability through alloying, hybrid organic-inorganic perovskites show promise as rear cell absorbers in tandem solar cells.