Potential of Chalcogenide Halide Bismuth Perovskites CH3NH3BiChI2 (Ch = S, Se,) as Solar Absorbers based on Theoretical Study

Organo lead halide perovskite has received a great deal of attention in the past couple of years due to its excellent optoelectronic properties. However, the presence of toxic lead in these materials is a significant concern for human health. Therefore, it is essential to select the elements for solar cell design that are environmentally friendly and conducive to human health. Many non-toxic alternatives can be used to solve this problem. Among those alternatives, Bismuth-based perovskite has become a promising alternative due to similar photovoltaic properties and enhanced environmental stability. Bismuth ternary based halide has interected due to their superior stability, but the main disadvantage is their wide band gap for single junction solar cells. The incorporation of the chalcogenide anions into bismuth chalcogenides was reported to have smaller bandgaps than that of the halide bismuth perovskites, which could reduce their bandgaps without affecting their photovoltaic properties. Band gap and dominant band to band absorption could be predictable from electronic property calculations using ground state density functional theory (DFT) as the lowest energy difference between the conduction band minimum (CBM) and the valence band maximum (VBM). As a result, for photovoltaic applications, the structural and band gap properties of mixed chalcogen and halogen anions, CH
3
NH
3
Bi (Ch, X)3 (Ch = chalcogen; X = halogen), were calculated using a combination of density- functional theory calculations. Results reveal that the band gaps of CH
3
NH
3
BiChI
2
S and CH
3
NH
3
BiChI
2
Se are 1.39 eV and 1.34 eV, which are in the range of band gaps required for photovoltaics.