| Summary: | 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<i><sub>n</sub></i><sub>+1</sub>Sn<i><sub>n</sub></i>Br<sub>3<i>n</i>+1</sub> and Cs<i><sub>n</sub></i>Sn<i><sub>n</sub></i><sub>+1</sub>Br<sub>3<i>n</i>+2</sub>, and studied their band structures and band gaps as a function of the number of layers (<i>n</i> = 1–5). The calculation results show that Cs<i><sub>n+</sub></i><sub>1</sub>Sn<i><sub>n</sub></i>Br<sub>3<i>n</i>+1</sub> has a direct bandgap while the bandgap of Cs<i><sub>n</sub></i>Sn<i><sub>n</sub></i><sub>+1</sub>Br<sub>3<i>n</i>+2</sub> can be altered from indirect to direct, induced by the 5<i>p</i>-Sn state. As the layers increased from 1 to 5, the bandgap energies of Cs<i><sub>n</sub></i><sub>+1</sub>Sn<i><sub>n</sub></i>Br<sub>3<i>n</i>+1</sub> and Cs<i><sub>n</sub></i>Sn<i><sub>n</sub></i><sub>+1</sub>Br<sub>3<i>n</i>+2</sub> decreased from 1.209 to 0.797 eV and 1.310 to 1.013 eV, respectively. In addition, the optical absorption of Cs<i><sub>n</sub></i><sub>+1</sub>Sn<i><sub>n</sub></i>Br<sub>3<i>n</i>+1</sub> and Cs<i><sub>n</sub></i>Sn<i><sub>n</sub></i><sub>+1</sub>Br<sub>3<i>n</i>+2</sub> was blue-shifted as the structure changed from bulk to nanolayer. Compared with that of Cs<i><sub>n+</sub></i><sub>1</sub>Sn<sub>n</sub>Br<sub>3<i>n+</i>1</sub>, the optical absorption of Cs<i><sub>n</sub></i>Sn<i><sub>n</sub></i><sub>+1</sub>Br<sub>3<i>n</i>+2</sub> was sensitive to the layers along the <i>z</i> direction, which exhibited anisotropy induced by the SnBr<sub>2</sub>-terminated surface.
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