Band Engineering of the Second Phase to Reach High Thermoelectric Performance in Cu2Se‐Based Composite Material

Abstract

AbstractHitherto, Cu2Se incorporated with a dispersed second phase shows extremely low thermal conductivity and excellent thermoelectric properties. However, the significant mismatch in electronic band structure between the second phases and the matrix often causes a deterioration of carrier mobility. In this work, based on density functional theory (DFT) calculations, the electronic band structure of the second phase is adjusted through doping S and Te. It is found that Cu2Se0.88S0.06Te0.06 has a highly similar electronic band structure to the Cu2Se matrix, which results in high carrier mobility and power factor in Cu2Se‐based composite materials. Additionally, the dispersed second‐phase Cu2Se0.88S0.06Te0.06, dislocations, and nanograins are observed in the Cu2Se/5 wt% Cu2Se0.88S0.06Te0.06 product, which leads to a substantial reduction in the thermal conductivity. Finally, high figure of merit (zT) values of 2.04 (by Dulong–Petit heat capacity) and 2.34 (by Differential Scanning Calorimetry (DSC) measured heat capacity) are achieved at 850 K, which are about 65% higher than that of Cu2Se in this work and comparable to the recently reported p‐type Cu2Se with outstanding performance.