Structural, optical and photocatalysis properties of sol-gel deposited Al-doped ZnO thin films

Nanostructured ZnO and Al doped ZnO (AZO) thin films were deposited onto glass substrates by a simple sol-gel dip coating technique. The effect of Al dopant on the crystal structure, surface morphology, optical and electrical properties of films were studied using powder X-ray diffractometer (XRD), scanning electron microscopy (SEM), UV-vis spectrophotometer, and four point probe technique respectively. The X-rays diffraction pattern showed the polycrystalline nature of pure and Al-doped ZnO thin films. The SEM images revealed that the films possess uniform distribution of identical nanoparticles throughout the surface and the grain dimension reduces with Al doping. The UV-visible transmission spectra showed that the Al substitution in ZnO leads to band gap narrowing together with a reduction in optical transmittance. The photocatalytic activity of these films was assessed through photocatalytic degradation kinetics of Methylene Blue (MB) dye and the degradation efficiency of the AZO films was compared with that of the ZnO films. The photocatalytic studies reveal that the AZO films exhibit better photocatalytic efficiency compared to the ZnO films. The enhanced photocatalytic activities of AZO thin films can be attributed to the charge trapping by Al dopant, enhanced surface area due to the decreased in grain size, and the band gap narrowing of AZO thin films.