The effects of Zn doping on the thermoelectric performance of Cu₁₂Sb₄S₁₃

In this study, first-principles electronic structure calculations and Boltzmann transport theories were used to understand the thermoelectric behavior of tetrahedrites. Calculations were performed on zinc (Zn)-substituted derivatives with zinc occupying each lattice site in the parent compound Cu₁₂Sb₄S₁₃ to study the zinc substitution mechanism and the relation between the zinc substitution site and thermoelectric performance. It was found that the most energetically favorable sites for zinc are the Cu(1) sites, and the next are the Cu(2) sites. Furthermore, the room-temperature Seebeck coefficient of the host was enhanced nearly 255 and seven times by zinc doping at Cu(1) and Cu(2) sites, respectively, owing to the decrease in carrier concentration and the increase in band effective mass, respectively. However, the electrical conductivity showed a marked decrease upon zinc doping at Cu(1) and Cu(2) sites, due to the decrease in carrier contribution and low mobility, respectively. As a result, Cu₁₂Sb₄S₁₃ compounds substituted with zinc at Cu(1) sites have a preferable optimizing power factor at room temperature. The optimizing power factor of the host could obtain approximately eight times improvement at room temperature upon zinc substitution at Cu(1) sites.