Effect of thickness and ageing time on optical properties of Zinc oxide film using sol-gel method

Zinc oxide (ZnO) is a semiconductor material which is widely used as thin films due to its
advantages in wide band gap, high electron mobility, large exciton binding energy and
others. The uniqueness of this semiconductor material is a different fabricating method
may differentiate its optical characteristics such as transmittance and absorbance
allowing it to suit various applications. In this research, ZnO thin films were prepared by
the sol–gel method on glass substrate. Zinc acetate dihydrate, isopropyl alcohol, and
monoethanolamine were used as a precursor, solvent, and stabiliser respectively. The
effects of ageing and thickness of ZnO on optical properties were discussed. The thickness of
thin films varied according to the number of dips in coating, which were 1 dip, 3 dips, 5
dips, or 7 dips. Meanwhile, the ageing duration varied between 12 hours, 24 hours, or 48
hours. The influence of thickness and ageing on the optical properties of ZnO were
investigated by ultraviolet-visible (UV-Vis) spectroscopy. When the thickness is increased,
the transmittance and the band gap are reduced due to compressive stress and lattice
defects. When the ageing duration is increased, the film becomes smoother.