First-principles computations of elastic, electronic, and optical properties of zero-dimensional perovskite Cs3BiX6 (X = Br, Cl)

Halogenated perovskite materials A(m)B(n)X(q) have attracted significant attention owing to their special photoelectric properties. The photoelectric properties of A(m)B(n)X(q) are strongly related to the geometric connectivity of their [BX] group constituents, which can be defined as their "dimensionality." As a newly synthesized compound, Cs3BiX6 (X = Br, Cl) has a crystal structure composed of cation Cs+ and [BiX6](3-) groups through ionic bonds. There are no links among [BiX6](3-), and thus Cs3BiX6 is considered to have a zero-dimensional structure. In this study, the elastic, electronic, and optical properties of Cs3BiX6 are studied in detail using first principles computations. The results show that Cs3BiX6 is a broadband direct semiconductor. The band structure of Cs3BiX6 without a spin orbit coupling effect is compared with that when considering the spin orbit coupling effect. It was found that the band gap of Cs3BiX6 decreases significantly owing to its spin orbit coupling effect. Five absorption peaks of Cs3BiBr6 are located at 4.88, 8.06, 10.34, 14.7, and 25.7 eV, which correspond closely to the wavelengths of 254, 154, 120, 84, and 48.4 nm within the ultraviolet region, respectively. Therefore, Cs3BiX6 has potential applications for use in ultraviolet photoelectric detectors.