Study on microstructural and electro-optical properties of sol–gel derived pure and Al/Cu-doped ZnO thin films

In this study, pure and doped ZnO thin films were prepared by sol–gel-based method and their electro-optical properties were investigated. For doping process, 1 at. % Al and Cu was incorporated in ZnO solution separately, and the thin films were prepared by dip coating method. The microstructure and morphology of calcined ZnO, Al-doped ZnO, and Cu-doped ZnO thin films were evaluated and compared by using various techniques X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and field emission scanning electron microscopy (FESEM). Results showed that nanostructured ZnO thin films with cross-linked nanoparticles (NPs) were formed, and the size of ZnO NPs increased with the Al and Cu doping. It was also found that the substitution and interstitial of Al and Cu dopants caused the instability of ZnO crystal structure and generation of extra point defects. Photoluminescence (PL) properties indicated that the dopants incorporation causes the decline of the PL intensity and the shift of the localized energy states of electrons and holes to lower energy levels. Evaluation of thin films in the UV–Vis range demonstrated that the transparency increased (>94%), and the band gap decreased to 3.08 and 3.06 eV with the incorporation of Al and Cu into ZnO thin films, respectively. The electrical conductivity also improved by Al and Cu doping of ZnO TFs.