Synthesis, Crystal Structure, and Optical Gap of Two-Dimensional Halide Solid Solutions CsPb2 (Cl1-xBrx)(5)

Exploring new perovskite-related solid-state materials and the investigating composition-dependent structural and physical properties are highly important for advanced functional material development. Herein, we present the successful hydrothermal synthesis of tetragonal CsPb₂Cl₅ and the anion-exchange phase formation of CsPb₂(Cl_1–xBr_x)₅ (x = 0–1) solid solutions. The CsPb₂(Cl_1–xBr_x)₅ crystal structures, which crystallize in the tetragonal system, space group I4/mcm, with parameters similar to those of CsPb₂Cl₅, have been determined by Rietveld analysis. The optical band gap was obtained by UV–vis spectroscopy, and the band structure was further calculated by the full-potential method within the generalized gradient approximation. It was revealed that the band gap in CsPb₂(Cl_1–xBr_x)₅ solid solutions can be tuned over the range of 4.5–3.8 eV by anion substitution.