The effect of post-deposition annealing conditions on structural and thermoelectric properties of sputtered copper oxide films

The development of thin-film thermoelectric applications in sensing and energy harvesting can benefit largely from suitable deposition methods for earth-abundant materials. In this study, p-type copper oxide thin films have been prepared on soda lime silicate glass by direct current (DC) magnetron sputtering at room temperature from a pure copper metallic target in an argon atmosphere, followed by subsequent annealing steps at 300 °C under various atmospheres, namely air (CuO:air), nitrogen (CuO:N) and oxygen (CuO:O). The resultant films have been studied to understand the influence of various annealing atmospheres on the structural, spectroscopic and thermoelectric properties. X-ray diffraction (XRD) patterns of the films showed reflexes that could be assigned to those of crystalline CuO with a thin mixed Cu (I) Cu (II) oxide, which was also observed by near edge X-ray absorption fine structure spectroscopy (NEXAFS). The positive Seebeck coefficient ( S ) reached values of up to 204 μV K −1 , confirming the p-type behavior of the films. Annealing under oxygen provided a significant improvement in the electrical conductivity up to 50 S m −1 , resulting in a power factor of 2 μW m −1 K −2 . The results reveal the interplay between the intrinsic composition and the thermoelectric performance of mixed copper oxide thin films, which can be finely adjusted by simply varying the annealing atmosphere. This study reveals the interplay between the composition and thermoelectric performance of mixed copper oxide thin films, which can be finely adjusted by varying the annealing atmosphere.