Thermoelectric Performance Enhancement in Off-Stoichiometric Ag–Se Alloys via Composition Imbalance and Vacancy Suppression

Abstract This study investigates the thermoelectric performance of off-stoichiometric Ag–Se alloys through composition-imbalance engineering. By varying the Ag-to-Se ratio, we successfully tuned the carrier concentration and mobility by suppressing Se-vacancy formation and reducing electron scattering. Simultaneously, grain refinement induced by excess Se enhanced phonon scattering, thereby lowering the thermal conductivity. Structural and phase analyses confirmed that Ag2Se remained the dominant phase across compositions. These findings highlight composition imbalance as a simple yet effective strategy for tuning thermoelectric performance in Ag–Se systems. This work offers a new pathway for designing high-performance, low-temperature thermoelectric materials.