Modulation mechanism of electronic and optical properties of Cs2SnX6 (X = Cl, Br and I) under hydrostatic or uniaxial pressure

The air-stable, low-toxicity double perovskite structure [Formula: see text] (X = Cl, Br and I) has attracted great attention due to its excellent potential in optoelectronic and photovoltaic applications. We used density functional theory to theoretically study the pressure response mechanism of double perovskite [Formula: see text]. The results show that pressure can effectively regulate the electronic structure and optical absorption properties of [Formula: see text]. When subjected to hydrostatic pressure ranging from 0 to 50 GPa, the bandgaps of [Formula: see text], [Formula: see text] and [Formula: see text] all exhibit a phenomenon of first decreasing and then increasing during the change. [Formula: see text] exhibits semimetallic properties when the valence band and conduction band begin to overlap under hydrostatic pressure of 2 GPa or higher. In addition, with increasing pressure, the optical absorption peak of [Formula: see text] shows a significant blue shift, and the absorption coefficient in the visible and near-infrared regions gradually increases. When a uniaxial pressure is applied to [Formula: see text] crystal, it significantly reduces in one direction and expands in the other two perpendicular directions. The structure changes from cubic phase to tetragonal phase. The optical absorption coefficient in the direction of pressure first increases and the others decrease.