NaSbSe₂ as a Promising Light-Absorber Semiconductor in Solar Cells: First-Principles Insights

Using density functional theory calculations, we studied the electronic, optical and defect properties of NaSbSe₂ systematically. It has an indirect gap (1.11 eV) which is slightly smaller than the direct gap (1.18 eV). The density of states analysis shows that the high optical absorption coefficient of NaSbSe₂ is attributed to the p-p transition from the valence band composed of Sb s/p + Se p states to the conduction bands composed of Sb p + Se p. Additionally, NaSbSe₂ exhibits intrinsic p-type conductivity due to the acceptor defects Na_Sb and V_Sb which always have the lowest formation energies under different chemical potential conditions. The ionization energy level (-2/0) of Na_Sb is very shallow and V_Sb can be ionized spontaneously once formed, so it is challenging to dope NaSbSe₂ to n-type. V_Se is a deep-level donor defect and may have high concentration under the Se-poor condition, so it may act as a recombination center and thus a Se-rich condition is required for achieving high solar cell efficiency. Our calculated results indicate that NaSbSe₂ may be a potential light-absorber semiconductor in thin-film solar cells.