Carrier–phonon coupling driven enhanced thermoelectric performance of Sn-substituted bismuth sulphide for intermediate-temperature applications

Abstract

Bismuth sulfide (Bi₂S₃) shows potential thermoelectric performance and has the exceptional properties of low cost, abundance, and eco-friendly nature. However, its poor electrical conductivity limits its thermoelectric properties, which can be improved by implementing various conventional techniques. Herein, one-pot synthesis along with hot-press sintering techniques were used to produce Sn-substituted Bi_2−xSn_xS₃ (x = 0, 0.050, 0.075, and 0.10) samples with orthorhombic structure. The high-valence Sn substitution augments the carrier density, which significantly enhances the electrical conductivity to 2789 S m⁻¹ for the Bi_2−xSn_xS₃ (x = 0.10) sample, along with the highest power factor of 192 μW m⁻¹ K⁻² at 623 K. Structural defects, including twin boundaries, stacking faults, and edge dislocations, as well as weak carrier–phonon coupling, play an important role in reducing the lattice thermal conductivity of the samples with respect to temperature. The improved electrical properties coupled with the low lattice thermal conductivity, lead to an improved thermoelectric zT value of 0.42 at 623 K for the Bi_2−xSn_xS₃ (x = 0.10) sample.