Enhanced thermoelectric performance of Bi2S3 by synergistical action of bromine substitution and copper nanoparticles

Bi₂S₃ thermoelectric materials have received extensive interests due to the ultrahigh abundance of sulfur element in the Earth׳s crust. However, the high electrical resistivity of pristine Bi₂S₃ leads to a low ZT value. In this work, incorporating small amounts of CuBr₂ into Bi₂S₃ system prepared by melting and spark plasma sintering can remarkably enhance the thermoelectric performance. Cu intercalation and Br substitution at sulfur sites contribute to a sharp decrease of electrical resistivity. Simultaneously, the strong point defects caused by Br alloying and formed Cu nanoparticles noticeably suppress the thermal conductivity. Collectively, the maximum ZT of 0.72 at 773K is obtained for the 0.5mol% CuBr₂ doped sample parallel to the press direction, which is the highest ZT value ever reported for Bi₂S₃ system, even comparable to the PbS-based thermoelectric materials.