Topological nature in cubic phase of perovskite CsPbI3: By DFT

In order to find out a better identification of halide perovskites as the materials with simple synthesis conditions and applicable in the electronics and solar cells industry, the present study have investigated the electronic properties, particularly band gap and band ordering of CsPbI3 perovskite in cubic phase and have evaluated their changes by means of exerting spin-orbit coupling and hydrostatic pressure. Calculations show that the values of band gap are 1.48 eV, 1.879 eV and 2.67 eV within GGA-PBE, GGA-mbj and GGA-newmbj approximations respectively. Whereas a drastic change occurs in electronic band gap due to applying the spin-orbit coupling effect and it leads to decreasing band gap to 0.29, 0.62 and 1.53 eV respectively which indicate the newmbj+soc results are in good agreement with experiment. Moreover, due to applying the hydrostatic pressure on electronic properties, the present study has investigated the changes in band gap and band ordering of band structure. In this regard, by increasing pressure, band inversion occurs between s-like and p(1/2) levels in valance and conduction bands in R-symmetry point in all three approximations with different pressure. Based on newmbj approximation, band inversion occurs in pressure about 6 GPa that is in agreement with other theoretical works. Furthermore, the occurrence of the band inversion in R-symmetry point contributes to the change in orbitals. Thus, it can be stated that the value Z(2) of topology coefficient is equal to one which proves the transition into the topological phase in this perovskite.