Improved thermoelectric properties of the β-Cu2+xSe/CuInSe2 multilayer films by layer interface scattering

The β-Cu_2+xSe/CuInSe₂ multilayer films with different modulation period were prepared and studied. The results showed that the deposited films possessed obvious layered structure. The room temperature carrier concentration, mobility, electrical conductivity and thermal conductivity decreased, but the Seebeck coefficient and power factor and relative thermoelectric figure of merit increased with reducing modulation period of deposited β-Cu_2-xSe/CuInSe₂ multilayer films. The linear reduction of carrier concentration and mobility and the decrease in thermal conductivity with modulation period was attributed to the scattering of carriers and phonons by layer interface and grain boundary, respectively. The sample with the smallest modulation period (160 nm) possessed the highest power factor of ∼0.74 at room temperature and ∼1.56 mW m⁻¹ K⁻² at 405 °C. The insertion of heterogeneous layer into films is an effective method to increase Seebeck coefficient and decrease thermal conductivity, thus increasing thermoelectric figure of merit of films.