Nucleation, Growth Mechanism, and Bifunctional Electrochromic Supercapacitive Properties of NiO Thin Films

Bifunctional devices combining display and energy storage capabilities are crucial for next-generation optoelectronic technology. This study investigates the application of nickel oxide (NiO) thin films for bifunctional electrochromic energy storage systems. The amorphous Ni(OH)₂ thin films were electrodeposited with a focus on their time-dependent properties. The Scharifker-Hills model revealed a mixed nucleation process during the electrodeposition. The deposited thin films were examined for their physicochemical properties using X-ray diffraction (XRD), micro-Raman spectroscopy, X-ray photoelectron Spectroscopy (XPS), and morphological studies. Rietveld refinement of the XRD pattern confirmed a cubic NiO polycrystalline phase, while XPS identified Ni³⁺ as the dominant oxidation state. Significant morphological changes were observed with the varying deposition time. The NiO electrode deposited for 120 minutes exhibited optimal characteristics, including the highest areal capacitance of 161.77 mF/cm^2, along with excellent cyclic stability of 96.5% even after 2000 CV cycles. The electrochromic study demonstrated optical modulation ranging within 55-82% at 532 nm, with a maximum coloration efficiency of 86.90 cm²/C. This research demonstrates the viability of NiO thin films as bifunctional electrochromic energy storage systems and the advancement of optoelectronic devices that integrate display and energy storage functionalities.