Comparison of the effects of Sr2+and Ca2+substitution on the structural and electronic properties of the perovskites CH3NH3Pb1-xYxI3 (Y--Sr, Ca) by using the Density Functional Theory

The Vienna ab-initio simulation package (VASP) and Density Functional Theory (DFT) calculation method are used to study the structural and detailed electronic properties through atomic substitution in the CH3NH3Pb(1x)Y(x)I3 (Y--Sr, Ca x = 0.125, 0.25, 0.50, 0.75, and 1.0) perovskites. We determined that the non-stoichiometric crystal structures were calculated as a distorted orthorhombic phase as predicted by the tolerance factor range 0.7 < t < 0.9. The bandgaps of the stoichiometric CH3NH3SrI3 and CH3NH3CaI3 compounds are calculated 3.261 eV (Q -> Gamma indirect) and 3.144 eV (Q -> Gamma indirect), respectively and they are very high for ideal photo absorbers. We were determined that the bandgap (Gamma -> Gamma direct) of the CH3NH3Pb0.875Ca0.125I3, CH3NH3Pb0.750Ca0.250I3, and CH3NH3Pb0.875Sr0.125I3 compounds are calculated 1.44 eV, 1.54 eV, and 1.525 eV respectively and are more suitable for ideal photo absorbers. It was seen that Ca2+ substitution was more successful than Sr2+ substitution.