Optical, structural and electrochromic properties of nickel oxide films produced by sol–gel technique

Nickel oxide films have been deposited from nickel acetate precursor using a sol–gel dip coating method, onto glass and conducting fluorine doped tin oxide (FTO) glass substrate. The direct energy gap ( E gd) values for the 2–10 layered films are in the range of 3.62 eV–3.72 eV. X-ray diffraction (XRD) analysis reveals that films consisting of 2–6 layers are amorphous, while films consisting of 8–10 layers are poly-crystalline with cubic grains of around 12 nm–20 nm and preferential growth along the (1 1 1) and (2 0 0) planes. Fourier Transform Infrared (FTIR) spectrum confirms the formation of Ni–O. Electrochromic properties of the nickel oxide coatings were studied using cyclic voltammetric (CV) technique. The 8 layered NiO films exhibit the anodic/cathodic diffusion coefficient of 16.7/5.73 × 10 −13 cm 2/s and the change in optical transmission is Δ T 630nm = 53% with a photopic contrast ratio of 2.87.