Porous Ag₂Se Fabricated by a Modified Cold Sintering Process with the Average zT Around Unity Near Room Temperature

Abstract Silver selenide (Ag₂Se) is a promising material for thermoelectric applications near room temperature. This work proposes a new fabrication route for bulk Ag₂Se via a modified cold sintering process (mCSP) to enhance its figure‐of‐merit (zT). Unlike conventional CSP, mCSP employs thiol‐amine (TA) as a liquid medium that completely undissolves Ag₂Se, leading to a free flow of the TA solution within interparticle channels. By sintering at temperatures above the boiling point of TA, the liquid evaporates, leaving behind a bulk Ag₂Se material with a tube‐like porous structure (open pores). These induced defects strongly influence thermoelectric properties of Ag₂Se, with a substantial increase in the Seebeck coefficient and decrease in electrical conductivity. The overall power factor of the mCSP sample with TA surpasses that of the control sample without TA, consistent with effective band modeling of Ag₂Se. Moreover, the created micropores during mCSP effectively suppresses the thermal conductivity, leading to a maximum zT above 1.0 at 400 K by optimizing mCSP parameters. Importantly, the average zT within the 300–400 K range is around unity, representing one of the highest reported values. Further optimization of mCSP parameters can enhance average zT beyond unity, making Ag₂Se more competitive with state‐of‐the‐art materials near room temperature.