Influence of deposition time on the structural, optical, and electrochemical properties of sprayed Co₃O₄ thin films

Abstract

In this study, Co₃O₄ thin films were synthesized via spray pyrolysis at deposition times of 10, 20, and 30 min. XRD analysis confirmed a cubic spinel structure, with crystallite sizes increasing from 14 to 28 nm, indicating improved crystallinity with longer deposition times. Raman spectra showed shifts toward higher wavenumbers, suggesting increased internal stress and film densification. SEM images revealed progressively denser and smoother surfaces, corroborated by EDX results showing higher Co and O concentrations. Optical transmittance decreased notably, particularly in the UV range, while absorbance increased. Two absorption edges associated with charge transfer transitions were observed; Tauc plots revealed two distinct optical band gaps. These decreased from 1.45 eV and 2.00 eV (10 min) to 1.39 eV and 1.89 eV (30 min), reflecting reduced quantum confinement and enhanced crystallinity. Electrical resistivity also decreased significantly, from 374 Ω·cm (10 min) to 10.9 Ω·cm (30 min), indicating improved film density and grain connectivity. Electrochemical measurements exhibited pseudocapacitive behavior with redox peaks characteristic of faradaic reactions. The 10-min film demonstrated the highest specific capacitance: 67 mF/g from cyclic voltammetry and 75 mF/g from galvanostatic charge–discharge. Extended deposition times altered the film morphology and structure, thereby influencing charge storage efficiency. These findings underscore the critical role of deposition time in tailoring electrochemical performance. Co₃O₄ films hold significant potential for energy storage applications when their structural and morphological properties are properly optimized.