Achieving high thermoelectric properties of Bi₂S₃ via InCl₃ doping

Bi₂S₃, with earth-abundant compositions and a low thermal conductivity, is regarded as a candidate thermoelectric material. In this work, Bi₂S₃ samples that were doped with x % mol InCl₃ were successfully fabricated via a mechanical alloying and spark plasma sintering process. InCl₃, as an n-type donor dopant, was added to the Bi₂S₃ system to improve its electrical transport properties and optimize its thermal conductivity. Upon doping, the electrical conductivity of Bi₂S₃ doped with 1 mol% InCl₃ reaches up to 62 Scm⁻¹, and the Seebeck coefficient maintains a relatively large value of −244 μV K⁻¹ at 673 K, which results in a maximum power factor of 363 μW m⁻¹ K⁻². Furthermore, due to a simultaneously reduced thermal conductivity at high temperature, a ZT peak of 0.57 is obtained at 673 K along the parallel to the press direction for the sample doped with 1.0 mol% InCl₃, which is almost four times higher than that of pristine Bi₂S₃ (0.14 at 673 K). The elastic properties and Debye temperature of Bi₂S₃ are also calculated to analyze the origin of the intrinsically low thermal conductivity and are compared to those of other thermoelectric materials with a low thermal conductivity.