Enhancing the thermoelectric performance of Cu2Se via Ag doping

Cu₂Se as a thermoelectric material has gained popularity in recent years because of the excellent properties resulting from its superionicity. In this study, Cu_2-xAg_xSe (x = 0, 0.05, 0.15, 0.25) samples were fabricated through the spark plasma sintering method, followed by a comprehensive microstructure and thermoelectric properties analysis. The results indicated that, when the doping amount of Ag is x ≥ 0.05, the CuAgSe phase is produced at room temperature, which introduces an energy filtering effect, resulting in an augmentation of the Seebeck coefficient and a reduction in the electrical conductivity. Ag doping leads to point defects, the disorder of cations, and the phase boundaries which increases phonon scattering, resulting in reduced thermal conductivity. At 773 K, the thermal conductivity decreases from 1.10 Wm⁻¹K⁻¹ for Cu₂Se to 0.41 Wm⁻¹K⁻¹ for Cu_1.75Ag_0.25Se. Compared to ZT ∼ 0.8 for the intrinsic Cu₂Se sample, the ZT of Cu_1.75Ag_0.25Se reaches 1.41 at 773 K, which is an increase of over 70 %.