Enhanced Thermoelectric Performance of Flexible Cu₂Se Films via Doping Iodine

Cu₂Se has become a highly promising thermoelectric material owing to its abundant elemental reserves, nontoxicity, and low thermal conductivity. In this work, flexible Cu₂Se_1-xI_x (x = 0, 0.02, 0.04, and 0.06) films were synthesized by a cost-effective and facile hydrothermal approach, followed by vacuum-assisted filtration and hot pressing, and the films were dense with well-crystallized Cu₂Se grains. The introduction of iodine provides an additional electron, acting as N-type doping and reducing carrier concentration. With the increase of x, the films exhibit a gradual reduction in electrical conductivity but a concurrent increase in the Seebeck coefficient. As a result, the Cu₂Se_1-xI_x film with x = 0.04 shows an optimal power factor of ∼566.9 μW m^-1 K^-2 along with remarkable flexibility at room temperature. In addition, the maximum output power of the six-leg flexible thermoelectric generator fabricated using the Cu₂Se_0.96I_0.04 film at a temperature difference of 22.8 K is 1.41 μW, with a power density of 4.02 W m^-2. This work presents an effective strategy for developing high-performance flexible Cu₂Se-based thermoelectric films.