An Enhanced Thermoelectric Performance of β-Cu ₂ Se/SnSe Multilayer Films by the Layered Structure

β-Cu2Se films exhibit high electrical conductivity and low thermal conductivity. However, their lower Seebeck coefficient hindered the improvement of the thermoelectric properties. To take advantage of the higher Seebeck coefficient of SnSe, we prepared and studied β-Cu2Se/SnSe multilayer films. Results showed that the columnar grains of the β-Cu2Se/SnSe multilayer films were refined with a decreasing modulation period. The reduction in carrier concentration and mobility with a reducing modulation period were attributed to the enhanced volume fraction of the SnSe phase and the strong scattering of layer interface and grain boundary. The electrical conductivity decreased and Seebeck coefficient increased with a reducing modulation period, leading to a tendency of first increasing and then decreasing for power factor. Sample S4, with a modulation period of 660 nm, achieved a maximum power factor of 3.04 mW·m–1·K–2 at 350 °C. After 1000 cycles under compressive and tensile bending with a radius of 3 mm, the electrical conductivity of the S4 multilayer film still remained at 87.4% and 82.5%, respectively. The excellent flexibility was attributed to the layer interface and refined column grain. A six-leg flexible thermoelectric generator (f-TEG) assembled by the S4 sample obtained maximum output power densities of 2.45 W·m–2 and 4.36 W·m–2 at temperature differences of 30 and 40 K, respectively. Correspondingly, the normalized maximum output power densities of the f-TEG reached 109.1 μW·m–1·K–2 and 121.3 μW·m–1·K–2. By introducing the SnSe heterogeneous interfacial layer, the carrier transport in the Cu2Se/SnSe multilayer films was effectively modulated, significantly enhancing their power factor and promoting their application in flexible thermoelectric devices.