Mechanical and Optical Properties of Cs4BX6 (B = Pb, Sn; X = Cl, Br, I) Zero-Dimension Perovskites

The crystal structures, elastic, anisotropy, and optical properties of zero-dimension perovskite Cs4BX6 (B = Pb, Sn; X = Cl, Br, I) compounds are investigated by first-principles calculations. The moduli of Cs4BX6 become lower in accordance with the order of Cl, Br, and I, and the moduli of tin-based compounds are larger than lead-based compounds. These two rules apply to other halide perovskites. Besides, Cs4BX6 compounds present obvious mechanical anisotropy and poor ductility. For optical properties, the alignment of PbX6 octahedra dictates the optical transition behavior of perovskite materials and pure Cs4BX6 compounds are candidates for ultraviolet devices due to the large band gaps. For the green emission of Cs4PbBr6, we believe the easily formed CsPbBr3 quantum dots or the defect level from vacancies, dislocations, and interstitial hydroxyl may be the main reason.