Theoretical study of tuning the band structure and absorption properties of two-dimensional Ruddlesden-Popper bilayer perovskite Cs3Sn2-yPbyX7 (X=Cl, Br, and I)

All-inorganic two-dimensional Ruddlesden-Popper halide perovskites have garnered considerable interest in the development of photodetectors because of their remarkable thermal stability and photoelectric characteristics. Nevertheless, the widely investigated compounds (Cs2PbI2Cl2, etc) possess a constant band gap, which restricts their potential for applications. Here, the first-principles method based on density functional theory is used to investigate the lattice, band structure, effective mass and optical properties of two-dimensional RuddlesdenPopper bilayer perovskite Cs3Sn2-yPbyX7 (X = Cl, Br, and I) under varying Pb concentrations y, halogen atoms X, and layer spacings d. The findings demonstrate their band gap, effective mass, and optical characteristics may be efficiently tuned by modifying y and X. y predominantly affects the absorption coefficient of visible light, X affects both visible and ultraviolet light. d slightly affects band gap but significantly affects the band shape. By analyzing their density of states, the physical mechanisms that the band structure changes with y, X and d are elucidated.