Thermoelectric and mechanical properties of Bi2S3−xSex polycrystals

Bi2S3 has the advantages of nontoxic and low-cost components, high Seebeck coefficient, and intrinsically low thermal conductivity, making it a promising thermoelectric material. However, its poor electrical conductivity limits its thermoelectric performance across all temperature ranges. To improve the conductivity of Bi2S3-based thermoelectric materials, Se, a Group VIA element similar to S, was chosen as an effective doping element to synthesise Bi2S3−xSex (x = 0, 0.1, 0.3, 0.5) bulk material via melting and spark plasma sintering. The room-temperature electrical conductivity of Bi2S2.7Se0.3 was approximately 24 S·cm−1, which is two orders of magnitude higher than that of pristine Bi2S3. At 623 K, Bi2S2.5Se0.5 exhibited an ultralow thermal conductivity of 0.5 µW·m−1·K−1. Thus, Se doping not only enhanced the electrical conductivity of Bi2S3 but also increased phonons scattering through Se substitution and interstitial Se, which significantly reduced the lattice thermal conductivity of Bi2S3. Consequently, the Bi2S2.7Se0.3 sample achieved an optimal ZT value of approximately 0.16 at 573 K, which is four times higher than that of the pristine Bi2S3 sample.