Effect of Different Annealing Temperatures on Structural, Optical, Morphological and Electrical Properties of Cu - ZnO Thin Films Prepared Using Sol—gel Spin Coating Techniques

Abstract

In this study, Cu - doped ZnO thin films were prepared at different annealing temperatures from Copper acetate precursor by sol-gel spin coating method for Photocatalytic Applications.  The films were characterized by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR).  The obtained powders were annealed under air in the range of  for Cu – ZnO. The surface morphological, structural, electrical and optical properties of the as-deposited ZnO films have been investigated as a function of Cu-doping level.  The thickness of the films was estimated by Fizeau fringes interference method which varied from 195 to 198 nm. The X-ray diffraction analysis indicated that the wurtzite structure was maintained for all samples and copper was successfully doped into ZnO at low TC. However, the formation of monoclinic CuO was observed at higher TC. For Cu – ZnO, the crystallite size increased with the annealing temperature from 15.86 to 24.24 nm. The isotherms obtained were type IV with a hysteresis type H 3, confirming the mesoporous behavior of the catalysts. The surface area was in the range of 35.1 to 8.66 /g. All the prepared catalysts mainly showed two emission regions: a sharp peak in the ultraviolet region and another broad peak in the visible region. The photocatalytic activity was achieved by the degradation of 300 mg/L malachite green (MG) aqueous solution under UV irradiation. The findings showed that the increased annealing of different concentration of Cu doped ZnO with CuO on the surface resulted in highly improved photocatalytic activity. Various optical constants such as absorbance, transmittance of the films have been studied. The values of transmittance are high in the visible and IR region and it is minimum in the UV region. Absorbance decreases with higher percentage of Cu concentration. The band gap of the films varied 3.21 to 3.05 eV. The resistivity gradually decreases with the increase of temperature, which indicates the semiconducting nature of the materials. Resistivity also increases with the increasing doping concentration. The conductivity decreases with the increasing of Cu concentration.