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(Cl1–xBrx)5 (x = 0–1) solid solutions. The CsPb2(Cl1–xBrx)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(Cl1–xBrx)5 solid solutions can be tuned over the range of 4.5–3.8 eV by anion substitution.