Pulsed Hybrid Reactive Magnetron Sputtering for High zT Cu₂Se Thermoelectric Films

Thermoelectric films on flexible substrates are of interest for the integration of thermoelectric in wearable devices. In this work, copper selenide films are achieved by a novel low‐temperature technique, namely pulsed hybrid reactive magnetron sputtering (PHRMS). A brief introduction to the basic chemistry and physics involved during growth is included to explain its fundamentals. PHRMS is a single‐step, room temperature (RT), fabrication process carried out in another ways conventional vacuum sputtering system. It does not require high‐temperature post‐annealing to obtain films with great thermoelectric performance. It is, therefore, compatible with polymeric substrates like Kapton tape. Several sets of films covering a large exploratory compositional range (from Cu/Se = 1 to 9) are deposited and their microstructure and thermoelectric properties are analyzed at RT. Power factors as high as 1.1 mW m⁻¹ K⁻² in the in‐plane direction and thermal conductivities as low as κ = 0.8 ± 0.1 W m⁻¹ K⁻¹ in the out‐of‐plane direction have been obtained for β‐Cu₂Se films. Consequently, a figure of merit of 0.4 at RT can be estimated under the assumption that for this polycrystalline cubic phase no additional anisotropy in the thermoelectric properties is introduced by the planar configuration. Moreover, PHRMS is also industrially scalable and compatible with the in‐line fabrication of other selenides.