Realizing Bi-doped α-Cu2Se as a promising near-room-temperature thermoelectric material

Copper selenide (Cu2Se) has been extensively studied as an eco-friendly thermoelectric candidate owing to the outstanding thermoelectric performance of its high-temperature β-phase. In this study, we propose that α-Cu2Se is also a promising thermoelectric material at near-room-temperature. We synthesize nanostructured Cu2-xSe via a facile solvothermal method, and densify the samples using Spark Plasma Sintering to maintain the small grain sizes. Although the as-prepared α-Cu2Se has intrinsically low lattice thermal conductivity, its high Cu deficiency leads to a high carrier concentration, therefore, a low thermoelectric performance. As an electron donor, bismuth can effectively compress the Cu vacancies of the as-prepared α-Cu2Se and in turn reduce its carrier concentration from 4.1 × 1020 to 2.0 × 1020 cm−3 at room temperature, achieving a significantly enhanced power factor and a reduced carrier thermal conductivity. Consequently, a zT of 0.43 at 373 K is obtained in Cu1.982Bi0.006Se, showing great potential in developing high-performance near-room-temperature α-Cu2Se-based thermoelectric materials.