Flexible Ag ₂ Se‐Based Thermoelectrics: Fundamentals, Processing, and Device Applications

ABSTRACT Ag 2 Se 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 Ag 2 Se‐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 Ag 2 Se‐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 Ag 2 Se‐based thermoelectrics in sustainable energy and wearable electronics.