Flexible Ag₂Se-Based Thermoelectrics: Fundamentals, Processing, and Device Applications.

Abstract

Ag₂Se is widely recognized as a leading n-type thermoelectric material for flexible and wearable applications owing to its narrow band gap, intrinsically low lattice thermal conductivity, and unusual room-temperature plasticity. This review systematically summarizes recent advances in Ag₂Se-based thermoelectrics, beginning with its fundamental crystal structures, defect chemistry, and electronic band features that govern its semiconducting and superionic transport behavior. Advanced performance-enhancement strategies are discussed in detail, including nanostructuring, stoichiometry tuning, doping, and the incorporation of inorganic or organic second phases. The progress in fabrication techniques, including vacuum-assisted filtration, screen printing, magnetron sputtering, thermal evaporation, and additive manufacturing, has also been highlighted. Scalability, flexibility, and mechanical durability are emphasized. Furthermore, the assembly and application of Ag₂Se-based flexible thermoelectric devices are reviewed, covering thermoelectric generators, Peltier coolers, electronic skins, and photo-thermoelectric hybrids. These devices demonstrate strong potential for energy harvesting, localized cooling, and smart sensing. Additionally, the challenges of device stability, large-area integration, and multifunctional system design are assessed. This review links material-level insights with device-level applications to accelerate the deployment of Ag₂Se-based thermoelectrics in sustainable energy and wearable electronics.