Realizing the High Thermoelectric Performance of Te-Free Bi₂S₃-Based Materials via Donor–Acceptor PbCl₂ and Nanodomains

Te-free Bi₂S₃-based thermoelectric (TE) materials present compelling prospects for ecofriendly and industrial scale-up applications, owing to their earth-abundant constituents, cost-effectiveness, and intrinsic nontoxicity. However, their low figure of merit (ZT) restricts their practical applications. In this study, both experiments and density functional theory calculations reveal that donor–acceptor PbCl₂ can simultaneously improve its electrical and thermal properties. In Bi₂S₃, Cl acts as the donor while Pb serves as the acceptor, and their competitive relationship leads to a trade-off between σ and S, thus increasing the power factor. Dense nanoscale structures (nanodomains) with the same structure but different light and dark paths, derived from the chemical composition fluctuation, are embedded in the PbCl₂-incorporated Bi₂S₃ matrix. Such a special structure leads to a low κ_lat of ∼0.33 W m^–1 K^–1 in the Bi₂S₃-1.5% PbCl₂ sample. As a result, a rather high ZT value of ∼0.82 at 673 K and an average ZT of 0.46 at 323–673 K are obtained for the PbCl₂-incorporated Bi₂S₃ sample, resulting in the superior TE performance of Bi₂S₃-based bulks. This work provides an effective strategy for enhancing TE properties in Bi₂S₃ semiconductors by nanodomain engineering.