Iodine Doping for the Tunable Phase Structure and Enhanced Thermoelectric Performance in Copper Selenide

The features of the phonon-liquid electron crystal (PLEC) are the keys to realizing excellent electrical and thermal transport properties of Cu2Se-based materials. Nevertheless, it is difficult to obtain the high-temperature cubic Cu2Se at room temperature, which inhibits the thermoelectric performance in a wide temperature range. Herein, a strategy of turning phase structure and thermoelectric performance in copper selenide was proposed by utilizing hydroiodic acid (HI) as a dopant in the hydrothermal reaction process. Iodine doping is effective in controlling the phase transition of copper selenide, causing the existence of a cubic phase in the copper selenide at room temperature. The electrical conductivity of I-doped Cu2Se is significantly increased owing to the variation of phase structure and carrier concentration. The power factor is therefore highly enhanced to 1925 μW m–1 K–2 for the Cu2Se-1 mL HI sample at 773 K. Ultimately, the average thermoelectric performance of the I-doped Cu2Se is improved in the whole temperature range. This study provides a novel path to controllably regulate the phase structure and thermoelectric properties of copper selenide, which might be worth promoting in other systems.