Electronic structure and absorption characteristics of two-dimensional perovskites Csn+1PbnCl3n+1 (n = 1, 2, and 4): Co-regulation of the number of layers and Ge doping concentration

The structures of monolayer (Cs₂PbCl₄), bilayer (Cs₃Pb₂Cl₇), and tetralayer (Cs₅Pb₄Cl₁₃) 2D CsPbCl₃ perovskites are constructed by cutting along the (001) crystal plane of CsPbCl₃. The lattice structure, band structure, density of states, and absorption coefficients of Cs_n+1Ge_nxPb_n(1-x)Cl_3n+1 (n = 1, 2, and 4) at various germanium (Ge) doping concentrations are calculated. By co-regulating the number of layers and Ge doping concentration, the range for band gap tuning can be significantly broadened, overcoming the limitations associated with using a single tuning parameter. Furthermore, the analysis of absorption coefficients shows that increasing the number of layers has a limited effect on the material's absorption at visible wavelengths but improves the overall absorption performance. Increasing the Ge doping concentration notably enhances the absorption capabilities across both the visible and ultraviolet (UV) spectra (>8 eV) of materials. In conclusion, the co-regulation strategy employed in this study provides a wider range of band gap and absorption capabilities tuning for Cs_n+1Ge_nxPb_n(1-x)Cl_3n+1, thereby significantly enhancing their potential and applicability in optoelectronics. Additionally, this study serves as an important reference for the construction and performance optimization of 2D perovskites.