Effect of film thickness on the electrical and the photocatalytic properties of ZnO nanorods grown by SILAR technique

In this work, Zinc oxide (ZnO) thin films were synthesised by the successive ionic layer adsorption and reaction (SILAR) technique at various number of cycles (10-50 cycles). The effect of film thickness on the structural properties, surface morphology, optical and electrical properties, and sunlight assisted photocatalytic activities through photocatalytic degradation of Methylene Blue (MB) dye of ZnO thin films were studied. The energy dispersive x-rays (EDX) analysis confirmed the presence Zn and O elements. The x-rays diffraction (XRD) pattern showed the polycrystalline nature of ZnO thin films and the crystallite size increases with film thickness. The SEM images showed that a greater film thickness resulted in the growth of hexagonal nanorods arrays. Atomic force microscopy (AFM) images revealed that the surface roughness increases with film thickness yielding in an enhanced specific surface area. The UV-visible transmission spectra showed that increasing film thickness results in band gap expansion from 3.15 eV to 3.31 eV together with a reduction in optical transmittance. The estimated sheet resistance and resistivity were found to be in the range of 1.34-7.1 omega sq-1 and 0.09-2.12 x10-1 omega.cm. The photocatalytic studies reveal that increasing film thickness leads to an improved photocatalytic efficiency of ZnO films. The enhanced photocatalytic activity of ZnO films is due to the increased surface area and low recombination rate of carriers charges (e-/h+), resulting from band gap expansion.