Exploring thermoelectric properties of hydrothermally synthesized Ag-doped SnS material

In recent years, tin sulfide (SnS), a layered chalcogenide material, has attracted considerable interest for its low toxicity, earth abundance, and promising thermoelectric (TE) properties. In this study, polycrystalline SnS samples—both undoped and Ag (2 at% and 4 at%)-doped were synthesized via a cost-effective and time-efficient hydrothermal method aimed at enhancing TE performance via nanostructuring and grain boundary scattering. X-ray diffraction (XRD) confirmed the phase purity, while Field Emission Scanning Electron Microscopy (FESEM) revealed sheet-like morphologies, and Energy-Dispersive X-ray (EDX) spectroscopy confirmed the elemental composition of the sample. UV–Vis spectroscopy indicated a reduced band gap of 1.28 eV for the 4 at% Ag-doped SnS, suggesting enhanced electronic properties. Fourier Transform Infrared (FTIR) spectroscopy identified the chemical bonds and functional groups present, and Thermogravimetric analysis (TGA) confirmed thermal stability up to 600 °C. Notably, undoped SnS exhibited the lowest thermal conductivity (0.18 W·m⁻¹·K⁻1 at 620 K), while Ag-doped samples showed slightly higher values due to increased carrier concentration (n) from hole doping. Electrical conductivity significantly improved after Ag doping, reaching 45.34 S/m at 620 K. However, the Seebeck coefficient values decreased for Ag-doped samples in comparison to undoped SnS due to the increase in n. To the best of our knowledge, the measured thermal conductivities are the lowest reported for doped SnS at this temperature. Our study presents that the hydrothermal method for synthesis is an effective and scalable approach for synthesizing SnS-based thermoelectric materials with ultralow thermal conductivity, making it a viable alternative to more expensive and complex fabrication techniques.