Structural and Optoelectronic Properties of Two-Dimensional Ruddlesden-Popper Hybrid Perovskite CsSnBr₃

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₊₁SnBr₃ and CsSn₊₁Br₃, and studied their band structures and band gaps as a function of the number of layers (n = 1-5). The calculation results show that Cs₁SnBr₃ has a direct bandgap while the bandgap of CsSn₊₁Br₃ 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₊₁SnBr₃ and CsSn₊₁Br₃ decreased from 1.209 to 0.797 eV and 1.310 to 1.013 eV, respectively. In addition, the optical absorption of Cs₊₁SnBr₃ and CsSn₊₁Br₃ was blue-shifted as the structure changed from bulk to nanolayer. Compared with that of Cs₁Sn_nBr₃, the optical absorption of CsSn₊₁Br₃ was sensitive to the layers along the z direction, which exhibited anisotropy induced by the SnBr₂-terminated surface.