Development of highly conductive and transparent copper doped zinc oxide thin films via 2-methoxyethanol modified sol–gel dip-coating technique

Nanocrystalline copper doped zinc oxide thin films were prepared via a modified 2-methoxyethanol sol–gel dip-coating technique at various concentrations of copper in the range 0–5 wt%. The X-ray diffraction analysis confirmed the copper doped zinc oxide hexagonal wurtzite structure. The copper ions interstitially substitute zinc ions in the hexagonal structure which resulted in the decrease of the crystallite size from 25 nm to 16 nm. A decrease in the lattice parameters was observed up to 2 wt% of copper ions followed by an increase. Scanning electron microscopy showed a homogenous distribution of the prepared films along the glass substrates. Energy dispersive spectroscopy confirmed the stoichiometry and high purity of the prepared films. The optimum optical band gap was achieved at 2 wt% of the copper ion concentration. The prepared films showed a high transparency in the visible region with an average value of 89%. The I–V characteristics showed Ohmic behavior up to 3 V. The electrical resistivity showed a lowest value (0.2 Ω cm) for the film doped with 2 wt% of copper.