Investigation of the Cathodic Potential Effect on the Morphological, Structural, and Optical Properties of Electrodeposited NiO Thin Films

In this study, nickel oxide (NiO) thin films were electrodeposited onto ITO substrates at various cathodic potentials (−1.30, −1.35, −1.40, and −1.45 V/SCE) using an aqueous solution of 0.05 M nickel sulfate, 0.1 M potassium chloride, and 0.5 M ethylenediaminetetraacetic acid at pH 12 and 70 °C. Cyclic voltammetry revealed the onset of NiO formation at −0.6 V. Chronoamperometry indicated a 3D diffusion-controlled nucleation and growth mechanism. Mott–Schottky analysis showed carrier concentration decreasing from 1.21 × 10 18 to 0.75 × 10 18 cm⁻ 3 with increasing potential, consistent with enhanced photoluminescence emission at 489 nm. Atomic force microscopy revealed rough, granular surfaces with non-monotonic grain size variation. X-ray diffraction confirmed the cubic NiO structure, with (111) crystallite sizes ranging from 27.8 to 16.3 nm. Raman spectroscopy verified the NiO phase via LO and 2LO phonon modes, characteristic of Ni–O vibrations. UV–Vis spectroscopy showed optical transmittance decreasing from 56% to 29% with increasing potential, while the band gap narrowed to 3.88 eV before slightly increasing. These findings demonstrate that deposition potential significantly influences the structural, morphological, optical, and electrical properties of NiO thin films, confirming electrodeposition as an effective elaboration method and highlighting their promising potential for high-performance devices.