Impacts of Cu deficiency on the thermoelectric properties of Cu2−XSe nanoplates

Non-stoichiometric CuSe is one of important thermoelectric candidates for intermediate temperature applications with intrinsically high performance at 800-1000 K. In this study, Cu-deficient CuSe nanoplates were synthesized by a facile and controllable solvothermal method and the impact of Cu deficiency on their corresponding thermoelectric performance was systematically investigated. It has been found that α-phased CuSe can be induced by a relatively high level of Cu deficiency (CuSe) in the as-synthesized CuSe nanoplates at room temperature. The Cu deficiency was also found to reduce the thermoelectric performances, but had no significant impact to the morphology of as-synthesized products. Overall, with the existence of full-spectrum phonon scattering mechanism benefited from the nanostructuring, the stoichiometric CuSe nanoplates showed an outstanding ZT of 1.82 at ∼850 K due to its significantly reduced thermal conductivity. With increasing the Cu deficiency, although the CuSe nanoplates showed a reduced ZT, such as 1.4 at 850 K for CuSe, it is still much higher than its bulk counterparts under the same temperature.