Modulation of secondary phases in hydrothermally grown zinc oxide nanostructures by varying the Cu dopant concentration for enhanced thermo power

In this study, we have successfully controlled the number of secondary phases in Zinc Oxide (ZnO) nano-structures by changing the concentration of Copper (Cu) atoms. Zinc Copper Oxide (Zn1-xCuxO) nanostructures with x = 0.1, 0.2, 0.3, 0.4 and 0.5 were grown by hydrothermal technique. The increased number of secondary phases with Cu concentration were resulted in the enhancement of Seebeck coefficient (72–124 μV/°C) and power factor (2.3 × 10−4 Wm−1K−2). The secondary phases are served as barrier therefore, filtered the low energy carriers at the interface of two secondary phases which resulted in the enhancement of Seebeck coefficient and electrical conductivity simultaneously. The emergence of secondary phases with Cu concentration was confirmed with the help supplementary measurements. X-Ray Diffraction (XRD) data is confirmed the formation of the wurtzite structure of ZnO along with the presence of Copper Oxide (CuO) based secondary phases. Furthermore, the intensity of secondary phases related XRD peaks were found to be increased with the increase of Cu concentration. Raman spectroscopy data was suggested that the intensity of E2 high mode was decreased due to the development of a number of secondary phases with Cu concentration. Scanning electron microscope images are shown the formation of hexagonal shaped nano structures. Fourier Transform Infrared Spectroscopy (FTIR) data was used to further confirm the presence of secondary phases in the grown Zinc Copper Oxide (ZCO) samples at higher concentration of Cu atoms. •Growth of Cu doped ZnO by hydrothermal method.•Different concentration of Cu creates secondary phases.•Thermoelectric properties enhanced due to the presence of secondary phases.•Presence of secondary phases verified by XRD, Raman spectroscopy and SEM.