Effect of Fe doping on the structural, morphological, optical, electrical, and photocatalytic properties of ZnO thin films deposited via spray pyrolysis

Abstract

Fe-doped ZnO thin films were synthesized onto glass substrates via spray pyrolysis, and the effects of Fe concentration from 0% to 6% on their structural, morphological, optical, electrical, and photocatalytic properties were systematically examined. X-ray diffraction analysis confirmed that all samples exhibit a polycrystalline hexagonal wurtzite crystal structure with a preferential orientation along the c axis. No secondary phases were detected within the detection limits of XRD, indicating successful incorporation of Fe into the ZnO lattice. The SEM images revealed notable variations in grain shape and distribution while energy-dispersive x-ray spectroscopy spectra verified iron incorporation, with its intensity increasing proportionally to doping concentration. Optical properties were studied using UV–Vis spectroscopy. The results show a decrease in transmittance (91%–49%) and a narrowing of the bandgap (3.22–3.17 eV) with increasing Fe content up to 4%. At 6% doping, a partial recovery in transmittance (71%) and a reduction in structural disorder were observed, while the bandgap increased to 3.19 eV, suggesting a saturation threshold in Fe incorporation. The electrical analysis of the films showed a decrease in electrical conductivity with increasing Fe concentration. Photocatalytic activity under sunlight was assessed via methylene blue degradation, showing a notable improvement upon Fe doping, and the degradation efficiency rose from 58% for the pure ZnO film to 67% for the 6% Fe-doped ZnO sample. While the overall efficiency is considered moderate, achieving this level of activation under sunlight is a significant result, given that ZnO typically requires UV light to exhibit high catalytic performance.