Ge doping collaboratively optimizes the thermoelectric properties and stability of liquid Cu2Se

Liquid Cu${}_2$Se thermoelectric materials hold significant potential due to their intrinsically low thermal conductivity. In this study, a series of Ge-doped Cu${}_2$Se samples were synthesized using mechanical alloying and spark plasma sintering techniques. The investigation focused on examining the effects of Ge doping on the thermoelectric performance and stability of Cu${}_2$Se. The introduction of Ge reduces Cu vacancies and promotes the formation of Cu${}_2$Se/Ge heterojunctions within the matrix. These heterojunctions act as filters for low-energy carriers, thereby optimizing carrier concentration. They also increase dislocation density, enhance phonon scattering, and reduce thermal conductivity. Furthermore, the Cu${}_2$Se/Ge interface forms a Schottky barrier, preventing the long-range migration of Cu${}^{+}$ ions, which enhances the material’s stability. As a result, the ZT value reached 2.44 at 823 K, representing a 114% improvement. Furthermore, the nano-secondary phase and grain refinement have increased the compressive strength by four times, providing crucial support for equipment engineering.