Interface‐Engineered Boosting of Phase Stability and Thermoelectric Performance of Ag 2 Se

ABSTRACT The development of advanced near‐room‐temperature thermoelectric materials is in high demand for low‐grade waste heat recovery applications. In this context, silver selenide (Ag 2 Se) emerged as a promising option that rivals the performance of traditional Bi 2 Te 3 while being more abundant. Nevertheless, its practical exploitation is constrained by its phase instability at elevated temperatures. Here, we present a composite engineering strategy that synergistically enhances phase stability and thermoelectric performance. The integration of secondary‐phase inclusions as pinning centers improves the phase stability of β‐Ag 2 Se and achieves a maximum figure of merit of 1.08 at 380 K, surpassing previously reported values for Ag 2 Se composites. This enhanced thermoelectric performance is attributed to the combined effects of energy filtering and phonon scattering mechanisms. For practical use, the fabricated single‐leg device delivers a power density of 26.6 mWcm −2 at ΔT = 80 K. These results highlight the promise of composite engineering as a scalable, viable approach to stabilizing and improving the performance of Ag 2 Se for waste‐heat recovery applications.