Layer-dependent photocatalytic efficiency of ZnO Thin films: kinetic analysis, structural insights and optical bandgap characterization using absorption spectrum fitting, Tauc’s plot, and Cody models

Abstract

This article has been allocated to studying microstructural features and optical properties of the polycrystalline thin ZnO films. ZnO thin films were deposited on glass substrates using a sol–gel dip-coating process with varied layer numbers (8, 10, and 12). Structural characterization via XRD confirmed a polycrystalline wurtzite structure with enhanced crystallinity as the number of layers increased and increasing the crystallite size from 34.8 ± 0.6 to 40.9 ± 0.7 nm. FE-SEM analysis revealed increased surface wrinkle size and reduced grain boundaries with thickness. Optical measurements showed high transmittance (> 80%) in the visible region and a slight reduction in bandgap energy from 3.17 ± 0.07 to 3.11 ± 0.03 eV with an increase in Urbach energy from 763.9 ± 5.3 to 847.3 ± 6.1meV. Photocatalytic performance was evaluated by degrading Rhodamine B under UV light, showing a significant enhancement in degradation rate from 0.034 ± 0.007 to 0.072 ± 0.008 min⁻¹ with increased film thickness. These findings highlight the potential of thickness-optimized ZnO films for environmental photocatalytic applications.