Thermoelectric properties of polycrystalline pristine and Pb-doped SnS materials using a conventional hydrothermal method

Tin Sulfide (SnS) has recently garnered significant attention due to its impressive Seebeck coefficient and low thermal conductivity. However, its electrical performance is notably poor, necessitating appropriate doping for its enhancement. To address this, we employed the conventional hydrothermal method to synthesize polycrystals of pristine and lead (Pb)-doped SnS samples to observe the impact on thermoelectric parameters. Utilizing FESEM, we obtained sheet sizes on the nanometer scale and observed irregular sheet-type morphology. HRTEM analysis confirmed the polycrystalline nature of the synthesized samples. Thermal stability assessment through thermogravimetric analysis (TGA) was conducted on all samples up to a temperature of 600 °C. The hydrothermal method resulted in nanostructuring that effectively suppressed the thermal conduction of low-frequency phonons, with increased phonon scattering attributed to the small grain size of particles. For pristine SnS nanoparticles, we determined the lowest total thermal conductivity (κ_T) to be 0.18 W (m-K)⁻¹, and the highest Seebeck coefficient reached 412.71 μVK⁻¹ at 620 K. In the case of the SnS–Pb(3 wt%) doped sample, there was a slight reduction in the total thermal conductivity (κ_T) compared to the pristine SnS sample. The pristine SnS sample exhibited the highest electrical conductivity (σ) of 0.21 S/cm at 620 K. In contrast, the SnS–Pb(3 wt%) doped sample demonstrated a twofold increase in electrical conductivity, measuring 0.38 S/cm at 620 K. This enhancement can be attributed to the increased carrier concentration resulting from the Pb(3 wt%) doping of SnS.