Enhanced Thermoelectric Performance of β-Ag₂Se/RGO Composites Synthesized by Cold Sintering Process for Ambient Energy Harvesting

Silver selenide (Ag₂Se) is a promising n-type thermoelectric material for near-room-temperature energy harvesting due to its high electrical conductivity and low lattice thermal conductivity. In this study, Ag₂Se-based composites were synthesized using a cold sintering process (CSP), enabling densification at low temperature under applied pressure. Reduced graphene oxide (RGO) was incorporated into the Ag₂Se matrix in small amounts (0.25–1.0 wt.%) to enhance thermoelectric performance. Structural analysis confirmed phase-pure β-Ag₂Se, while SEM and TEM revealed homogeneous RGO dispersion and strong interfacial adhesion. RGO addition led to a reduced carrier concentration due to carrier trapping by oxygen-bearing functional groups, resulting in decreased electrical conductivity. However, the absolute Seebeck coefficient increased with RGO content, maintaining a balanced power factor. Simultaneously, RGO suppressed thermal conductivity to below 0.75 W m⁻¹ K⁻¹ at room temperature. The optimal composition, 0.75 wt.% RGO, exhibited the highest average zT of 0.98 across the temperature range from room temperature to 383 K. These results demonstrate that combining the CSP with RGO incorporation offers a scalable and cost-effective strategy for enhancing the thermoelectric performance of Ag₂Se-based materials.