Sputter-Deposited Nano-porous ZnO Electrode for Highly Efficient Optoelectronic and Solid-State Energy Storage Devices

The present work demonstrates a direct sputtering synthesis approach for a nano-porous ZnO electrode on indium tin oxide (ITO) substrate. Various sophisticated material characterization analytical tools confirmed successful growth of the electrode. The electrochromic and electrochemical performance of the fabricated electrode was examined using two well-known techniques, UV–Vis spectroscopy and cyclic voltammetry (CV). Contact angle measurement for droplet stability revealed dynamic wetting behavior (87.2° ≥ θ_w ≥ 57.9°) and surface energy variation (50.02 ≥ γ_SL ≥ 18.48 mN/m). This nano-porous structure-based electrochemically active electrode exhibited scaled electrochromic and capacitive performance, i.e., good optical transmittance modulation (24%), optical density change (ΔOD) (0.206), coloration efficiency (31.8 cm²C⁻¹), and specific (331 F/g) and areal capacitance (79.4 mF cm⁻²). The cyclic durability of the electrode was found to be highly stable, which may be attributed to a significant drop in the specific capacitance (14.7%) after 5000 cycles. These results indicated that this porous nanostructure promotes the penetration of aqueous electrolyte and alleviates diffusion. The results confirm the excellent prospects of novel and cheap ZnO-based electrodes with integrated functionality for efficient optoelectronic and solid-state energy storage devices.