Fast, Simple, and Cost-Effective Fabrication of High-Performance Thermoelectric Ag2Se through Low-Temperature Hot-Pressing

Silver selenide (Ag₂Se) is a promising thermoelectric material for near-room temperature applications. This study proposes a fast, simple, and cost-effective method for producing high thermoelectric performance bulk Ag₂Se. Ag₂Se powders were synthesized from Ag and Se powders via a one-hour wet ball milling process, followed by the fabrication of bulk pellets through low-temperature hot-pressing (130–250 °C) with a mere 0.5-hour holding time. Both Ag₂Se powders and bulk pellets exhibited a single phase of Ag₂Se with an orthorhombic structure. Moreover, uniform compositional distribution with the stoichiometric Ag : Se ratio was observed in all samples. Microstructural analysis revealed distinct grain boundaries in samples hot-pressed below 190 °C, transitioning to grain coalescence was at 190 °C and 250 °C. The thermoelectric and transport measurements demonstrated that the electrical conductivity decreased and the Seebeck coefficient increased with hot-pressing temperatures from 130 °C and 190 °C primarily due to reduced carrier concentrations. Thermal conductivity decreased with increasing hot-pressing temperatures up to 190 °C, attributed to the weak chemical bonding of Ag₂Se and the presence of defects. This combination resulted in a peak zT over 1.0 at 300 K, with an average zT close to 1.0 from 300 to 380 K. In comparison to other reported synthesis methods, the present approach offers significantly reduced processing time, simplicity, and cost-effectiveness. Despite lower temperatures and shorter processing times, the method produces Ag₂Se with zT values comparable to more intricate techniques. This fabrication route holds the potential for scalable mass production in the future.