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 (Egd) 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 cm2/s and the change in optical transmission is ΔT630nm = 53% with a photopic contrast ratio of 2.87.