First-principles study for comparison of the electronic and optic bandgaps of the CH3NH3Pb1-xYxI3 (Y=Bi, x=0.00, 0.125) and CH3NH3Pb1-xYxI3 (Y=Ca, Sr, x=0.125, 0.250) perovskites

We computed the optical bandgaps of the CH3NH3Pb(1-x)Y(x)I3 (Y=Bi, x = 0.00, 0.125) and CH3NH3Pb(1-x)Y(x)I3 (Y=Ca, Sr, x = 0.125, 0.250) perovskite crystal structures using optical arguments such as the imaginary part of the dielectric function e2(w), absorption coefficient (?), the zero-crossing point of the (?hv)2 versus (hv). Density Functional Theory (DFT) calculations and the Vienna ab-initio simulation package (VASP) are used in theoretical calculations. The optical bandgap of the stoichiometric CH3NH3PbI3 phase calculated as 1.694 eV is in agreement with both experimental and theoretical studies. The optical bandgaps of the non-stoichiometric phases are calculated as 1.358 eV, 1.493 eV, 1.537 eV, 1.503 eV, and 1.588 eV, respectively. These optical bandgaps results are reported for the first time in this study.