Impact of alkaline-earth doping on electronic properties of the photovoltaic perovskite CsSnI: insights from a DFT perspective.

The oxidation of Sn(II) to the more stable Sn(IV) degrades the photovoltaic perovskite material CsSnI; however, this problem can be counteracted alkaline-earth (AE) doping. In this work, the electronic properties of CsSnAEI, with = 0 and 0.25, and AE = Mg and Ca, were investigated Density Functional Theory. It is proven that the synthetic reactions of all these perovskites are thermodynamically viable. Besides, a slight strengthening in the metal-halide bonds is found in the Mg-doped perovskite; consequently, it exhibits the greatest bulk modulus. Nevertheless, the opposite occurrs with the Ca-doped perovskite, which has the smallest bulk modulus due to the weakening of its metal-halide bonds. The calculated bandgaps for CsSnI, Mg-doped and Ca-doped perovskites are 1.11, 1.32 and 1.55 eV, respectively, remaining remarkably close to the best photovoltaic-performing value for single-junction solar cells of 1.34 eV. Nevertheless, an indirect bandgap was predicted under Mg-doping. These results support the possibility of implementing AE-doped perovskites as absorber materials in single-junction solar cells, which can deliver higher output voltages than that using CsSnI. Finally, it was found that Sr or Ba doping could result in semiconductors with bandgaps close to 2.0 eV.