Enhancing Photocatalysis, Self-Cleaning, and Waveguiding in Ni-Doped ZnO Thin Films for Optoelectronic and Environmental Remediation Applications

This study investigates the effects of nickel (Ni) doping on the structural, optical, and photocatalytic properties of ZnO thin films, which are crucial for applications in optoelectronics, photocatalysis, and self-cleaning. ZnO thin films were deposited using spray pyrolysis at a substrate temperature of approximately 450 °C, with Ni concentrations of 3, 6, 9, and 12 wt.%. X-ray diffraction analysis revealed that Ni doping significantly influenced the crystallinity of the films, with the average grain size increasing to 43.65 nm at 3% Ni doping and up to 52.52 nm at 9% Ni doping, indicating enhanced crystallinity. Compressive stress was observed at 3% (lattice constant = 0.5210 nm) and 12% (lattice constant = 0.5540 nm), while tensile stress occurred at 6% (lattice constant = 0.5180 nm) and 9% (lattice constant = 0.5170 nm). The optical properties showed a decrease in transmittance from 83.8% for undoped ZnO (ZN0) to 81.3% for 12% Ni doping and a narrowing of the bandgap from 3.202 eV (ZN0) to 3.261 eV (ZN12). The films’ refractive index decreased with increased Ni doping, from 1.9670 for ZN0 to 1.9621 for ZN12, indicating changes in the material’s electronic structure. M-lines spectroscopy revealed that Ni doping improved waveguiding properties, with a peak thickness of 382.08 nm at 12% Ni doping. Additionally, wettability measurements showed that 3% Ni-doped ZnO exhibited the most hydrophilic surface (contact angle = 68.8°), while higher Ni concentrations decreased wettability, reaching 75.2° at 12% Ni doping. Photocatalytic testing revealed that 3% Ni-doped ZnO (ZN3) exhibited photocatalytic efficiency (73.3%) close to that of undoped ZnO (ZN0), making it suitable for dye degradation applications. These findings suggest that Ni-doped ZnO films are promising for a wide range of applications, although further research is needed to evaluate their long-term stability.