BaSi₂as a promising low-cost, earth-abundant material with large optical activity for thin-film solar cells: A hybrid density functional study

Employing a hybrid density functional theory, we reveal the origin of the large absorption coefficient in BaSi2, which is roughly two to eighty times larger at ħω − Eg = 0.5 eV than other conventional absorbers such as Si, GaAs, CdTe, CuInSe2, and Cu2ZnSnS4. This is explained on the basis of the electronic band structure of BaSi2, whereby the lowest conduction band (CB) has a small dispersion, owing to the localized Ba-d states, resulting in flat bands. Consequently, these flat bands contribute to a wide range of optical absorption in the low-energy region and lead to high optical activity in BaSi2.