Effect of substrate temperatures, spray rates, solution volumes, and nickel concentration on structural and optical properties of NiO thin films prepared by spray pyrolysis

Nickel oxide thin films were successfully percipitated at different substrate temperatures (440, 460, 480, and 500 oC), spray rates (1, 2.5, 5, and 7.5 ml/min), solution volumes (50, 100, 150, and 200 ml), and nickel concentration (5, 10, 15, and 20 at.%) glass substrates using NiCl2.6H2O as precursor and the spray pyrolysis technique. The structural and  optical properties of the thin films were characterized. They show a polycrystalline nature with a cubic structure of single-phase NiO and peaks related to (111), (200), and (220) with a preferential orientation along (111). The morphology of the NiO thin films resembles that spherical grains on the entire surface, with an average roughness ranging from 28.71 to 105.63 nm, depending on the deposition conditions. The range of the optical gap and Urbach energy were measured to be 2.55 to 3.49 eV and 0.41 to 0.55 eV, respectively.