Effect of a cobalt complex on the structural, optical, electrical, and anti-reflective properties of ZnO thin films

Minimizing surface light reflection is crucial for enhancing the efficiency of solar cells, necessitating the development of advanced anti-reflection coatings. This study investigates the structural, optical, electrical, and anti-reflection properties of ZnO thin films doped with commercially available cobalt acetate tetrahydrate and a synthesized cobalt complex (C16H11N3Cl2Co). The films were fabricated using the Sol-Gel spin coating method and characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–Vis spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), and energy-dispersive X-ray fluorescence (ED-XRF). The XRD analysis revealed a hexagonal wurtzite structure, with crystallite sizes ranging from 25.41 nm to 64.65 nm depending on the cobalt content. UV–Vis spectroscopy indicated a bandgap shift from 2.68 eV (pure ZnO) to 3.10 eV, with the synthesized cobalt complex promoting a higher bandgap. The refractive index decreased from 2.427 to 2.299 as the doping concentration increased. Electrical conductivity dropped from 1.5 × 10−7 S/cm for pure ZnO to ∼10−10 S/cm for the highest cobalt concentration. Effective atomic numbers (Zeff) decreased with increasing cobalt content, with values ranging between 13.255 and 13.453. Anti-reflection performance improved, with ZnO films doped with 6 wt% cobalt complex achieving a 7.97 % reduction in reflectance compared to those doped with commercial cobalt. These results demonstrate that cobalt-doped ZnO thin films, particularly those incorporating the synthesized cobalt complex, offer superior anti-reflection properties, making them promising candidates for enhancing solar cell efficiency.