Electronic and Optical Properties of Low- Concentration Ge Doping and Substitution of Sn and Ge for CsPbI3

The structure, electronic and optical properties of inorganic perovskite materials CsBI3 (B= Pb, Sn, Ge) are analyzed based on the first principle by Siesta software. First, a stable material structure is obtained using the GGA-PBE and GGA- PBEsol methods. Then, the bandgap of the material is analyzed based on two density functional methods GGAPBE and GGA-BLYP. This work simulates the material strain by changing the lattice constant of the material, showing that the bandgap increases with an increase in the lattice constant. Moreover, doping with Ge can decrease the bandgap of supercell CsPbI3. When doped with low-concentration Ge, the band gap of the material was found to reduce by 0. 7% to 3. 8%. Finally, from the absorption spectrum, it can be seen that the absorption coefficients of CsPbI3 and CsGeI3 are close to 6x10(5) cm(- 1), and the absorption peak of CsPbI3 is approximately 350 nm and that of CsGeI3 is approximately 410 nm. However, the absorption coefficient of CsSnI3 is close to 4. 75x10(5) cm(-1), and the absorption peak is approximately 350 nm.