First-principles study of photoelectric properties of CsSnBr<sub>3</sub> under hydrostatic pressure

As an important perovskite solar cell (PSC) material, CsSnBr₃ has been widely studied. Based on the density functional theory (DFT), the photoelectric properties of CsSnBr₃ are studied by using the first-principles at different hydrostatic pressures. It is found that CsSnBr₃ has an optimal optical band gap value of 1.34 eV under a pressure of 2.6 GPa, so only the photoelectric properties of CsSnBr₃ under the hydrostatic pressure of 0 GPa and 2.6 GPa are studied, respectively. When the pressure is 2.6 GPa, CsSnBr₃ has larger values of dielectric, conductivity, absorption coefficient and refractive index, the red-shifted absorption spectrum, and relatively small effective mass of electron and hole and exciton binding energy, indicating that CsSnBr₃ is an efficient light absorbing material. According to the triple calculations of Born-Huang stability standard criterion, the tolerance factor <i>T</i> and phonon spectrum with or without virtual frequency, it is found that CsSnBr₃ is stable under the pressure of 0 GPa and 2.6 GPa. According to the elastic modulus value of CsSnBr₃ before and after pressure, it can be seen that the CsSnBr₃ is soft, with good ductility and anisotropy. The Debye temperature and heat capacity of CsSnBr₃, soon after it has been pressured, tend to be stable and are independent of temperature. The enthalpy and entropy increase with temperature increasing, and the increased amplitude is larger than those of the unpressured CsSnBr₃. Gibbs free energy shows a decreasing trend, and the decrease is slightly faster when unpressured. This study shows that CsSnBr₃ is a good photoelectric material after having been pressured hydrostatically, which is suitable for perovskite solar cells.