Spray Pyrolysis-Derived Cobalt Oxide Thin Films: Synthesis and Optical Property Evaluation

Abstract

This study presents a simple and cost-effective approach for synthesizing cobalt oxide (Co₃O₄) thin films on glass substrates using a homemade spray pyrolysis technique. The investigation centers on how thermal treatment affects the optical properties and band gap of Co₃O₄ thin films, synthesized with varying precursor concentrations and layer thicknesses. As-synthesized Co₃O₄ thin films stand out for its remarkable catalytic activity, thermal stability, and optical characteristics attributed to variable oxidation states of Co, strong Co-O bonds, and a narrow band gap. X-ray diffraction (XRD) analysis confirmed the formation of crystalline Co₃O₄, with crystallite size increasing from 12.52 nm (non-annealed) to 16.23 nm after annealing. Optical transmittance data were used to determine the band gap energies, revealing that non-annealed films possessed higher band gap values. This indicates a consistent decrease in band gap energy with increasing annealing temperature. Overall, the spray pyrolysis method offers practical advantages for thin film fabrication, including operational simplicity, scalability, and low production cost.