Enhanced Supercapacitive Performance of Fe-Doped CuO Nanostructured Thin Films Synthesized via Ultrasonic Spray Pyrolysis

CuO nanostructured thin films, both undoped and Fe-doped, were successfully deposited onto ITO substrates using the ultrasonic spray pyrolysis (USP) technique. The structural, morphological, optical, and electrochemical characteristics of CuO were systematically investigated as a function of Fe incorporation. X-ray diffraction results verified the formation of the monoclinic CuO phase. However, noticeable changes in peak intensity and crystallite size were observed after Fe addition. Moreover, SEM images revealed that Fe doping modified the surface morphology and promoted the growth of larger polyhedral grains. Elemental mapping further verified the uniform distribution of Fe within the CuO matrix. Optical measurements showed an increase in absorbance and a slight widening of the band gap with increasing Fe content. In addition, photoluminescence intensity decreased after doping, indicating changes in defect structure and charge recombination behavior. The electrochemical performance was evaluated using cyclic voltammetry, galvanostatic charge–discharge, and impedance spectroscopy in 1 M KOH electrolyte. The Fe-doped CuO electrodes exhibited significantly enhanced specific capacitance compared to undoped CuO. This improvement was attributed to increased surface activity and improved charge transfer properties. Thus, Fe incorporation effectively enhanced the electrochemical behavior of CuO thin films, making them promising candidates for supercapacitor applications.