Recent progress in Cu 2 Se thermoelectric materials: fundamentals, performance, and stability

Abstract Thermoelectric technology converts waste heat directly into electricity, enabling sustainable energy recovery. Cu 2 Se is a standout high-temperature thermoelectric material, delivering high efficiency through superionic Cu transport consistent with the phonon-liquid electron-crystal concept. In the past decade, performance has been boosted by micro/nanostructuring, compositional control, doping, and composite architectures, yet operational instability driven by Cu migration remains the key obstacle to deployment under realistic thermal gradients. This review summarizes recent progress in Cu 2 Se thermoelectric materials with a particular emphasis on connecting fundamental ion-transport and resulting high thermoelectric performance to stability challenges and engineering solutions. We outline crystal structures, phase transitions, Cu-ion transport mechanisms, and synthesis routes, then survey strategies to enhance power factor and suppress thermal conductivity, including nanoscale engineering, compositional control, doping, compositing, and hybrid approaches. We further review stability engineering, including ion confinement, ion-blocking barriers, and defect/phase stabilization. Finally, we conclude by outlining perspectives and future research directions for advancing Cu 2 Se toward robust, application-relevant thermoelectric devices.