High Thermoelectric Figure of Merit (zT) in β-Ag2Se via Aliovalent Doping

Abstract

High-performance thermoelectric materials are essential for efficient low-temperature (300–400 K) heat energy harvesting, with n-type Ag₂Se being a promising candidate. To further enhance the thermoelectric figure of merit (zT) of Ag₂Se, aliovalent doping has emerged as a key strategy. However, achieving wet-chemical aliovalent doping of Ag₂Se at ambient temperature has proven challenging. In this work, a high zT_max of 1.57 at 398 K is reported for an optimally Cd(II)-doped Ag₂Se sample, specifically in the structurally phase-pure Ag_1.98Cd_0.02Se, which is successfully synthesized via an aqueous-based method at room-temperature (300 K). The Ag_1.98Cd_0.02Se sample also exhibits an impressive average zT_avg of 1.12 over the temperature range of 315–400 K. Density functional theory (DFT) calculations for both the pristine and doped samples reveal significant changes in the electronic band structures, including notable modulations in the density of states near the Fermi energy, particularly for the Ag-3d states. The remarkable thermoelectric performance of Ag_1.98Cd_0.02Se is attributed to an optimization of charge carrier induced by the Cd(II)-doping.