Structural and Optoelectronic Properties of Two-Dimensional Ruddlesden–Popper Hybrid Perovskite CsSnBr(3)

Ultrathin inorganic halogenated perovskites have attracted attention owing to their excellent photoelectric properties. In this work, we designed two types of Ruddlesden–Popper hybrid perovskites, Cs(n)(+1)Sn(n)Br(3n+1) and Cs(n)Sn(n)(+1)Br(3n+2), and studied their band structures and band gaps as a function of the number of layers (n = 1–5). The calculation results show that Cs(n+)(1)Sn(n)Br(3n+1) has a direct bandgap while the bandgap of Cs(n)Sn(n)(+1)Br(3n+2) can be altered from indirect to direct, induced by the 5p-Sn state. As the layers increased from 1 to 5, the bandgap energies of Cs(n)(+1)Sn(n)Br(3n+1) and Cs(n)Sn(n)(+1)Br(3n+2) decreased from 1.209 to 0.797 eV and 1.310 to 1.013 eV, respectively. In addition, the optical absorption of Cs(n)(+1)Sn(n)Br(3n+1) and Cs(n)Sn(n)(+1)Br(3n+2) was blue-shifted as the structure changed from bulk to nanolayer. Compared with that of Cs(n+)(1)Sn(n)Br(3n+1), the optical absorption of Cs(n)Sn(n)(+1)Br(3n+2) was sensitive to the layers along the z direction, which exhibited anisotropy induced by the SnBr(2)-terminated surface.