First-Principles Study on the Direct Bandgap Double Perovskite Series Cs₂LiInX₆(X = F, Cl, and Br)

A molecular crystal structure model of the lead-free halide chalcogenide semiconductor Cs₂LiInX₆ (X = F, Cl, and Br) was established, and its energy band, density of states, optical properties, and thermodynamic properties were calculated using the first nature principle and the effect of different pressures on the bandgap of Cs₂LiInX₆ (X = F and Cl, Cs₂LiInF₆ with a bandgap of 7.359 eV, Cs₂LiInCl₆ with a bandgap of 5.098 eV, and Cs₂LiInBr₆ with a bandgap of 3.755 eV). The absorption of light is mainly due to the transition of halide ions from p- to s-orbitals. The p- and In-s orbitals of halide ions play a major role in light harvesting. Cs₂LiInCl₆ has low sensitivity to relative pressure and is stable at a 0-100 GPa pressure. In the structure of Cs₂LiInX₆ (X = F, Cl, and Br), changing the halogen atom can effectively improve its optical properties. Cs₂LiInCl₆ and Cs₂LiInF₆ are considered as the most promising candidates for UV detectors. Cs₂LiInF₆ has a large forbidden band width and a high Debye temperature and shows a high photoluminescence quantum yield in the field of phosphors with great potential in the field of phosphors with high photoluminescence quantum yields. This study is a positive reference for the preparation of lead-free chalcogenide-type ultraviolet detectors with excellent performance.