Effect of post annealing temperature upon the electrical properties and kinetics of photocatalytic degradation by dip coated ZnO thin film

ZnO thin films (TFs) were successfully coated onto glass substrates using the sol-gel dip-coating technique, followed by annealing at various temperatures ranging from 300 to 550 °C, in 50 °C increments. This study explores how annealing temperature influences the electrical, self-cleaning, and photocatalytic properties of these films under sunlight irradiation, supported by detailed structural, surface morphology, and optical analyses. XRD results confirm that all films exhibit a polycrystalline hexagonal wurtzite structure with a dominant (002) orientation, and the crystallite size grows as the annealing temperature increases. SEM images reveal a uniform, crack-free surface morphology, while AFM analysis indicates a low but increasing surface roughness with rising temperature. Optical measurements in the UV-VIS range demonstrate exceptionally high transmittance values (up to 99%), with the optical band gap shifting slightly from 3.27 to 3.31 eV, and Urbach energy around 60 meV, suggesting minimal defects. Electrical conductivity showed a moderate increase from 3.82x10⁻³ to 1.37x10⁻¹ Ω.cm⁻¹ as the annealing temperature rose. Additionally, all films exhibited excellent hydrophilicity, with contact angles ranging from 47.50° to 65.66°, making them ideal for self-cleaning applications. Photocatalytic testing showed that the film annealed at 450 °C exhibited the highest efficiency for methylene blue degradation under sunlight irradiation, positioning it as a promising candidate for environmental remediation applications.