In this thesis, the seed layer of nickel oxide (NiO) nanoparticles (NPs) was fabricated and deposited by spray pyrolysis process on glass substrates. The solution of seed layer extract was deposited on the glass substrate twice at an angle of 90° for 5 seconds at a distance of 20 cm, and the biosynthesized sample was prepared using a leaf extract from a fresh Leek leaf. These seed layers grow in NiO NPs solutions at different pH values and concentrations for 4 hours. The two primary green growth solutions differed in their pH and nickel concentration ratios for cultivating the seed layer of NiO NPs using the green method. The effects of different pH ratios and NiO nanoparticle concentrations on average size, shape, distribution, crystal structure, functional groups, optical properties, chemical composition, and energy band gap have been investigated in detail for the first time using the green synthesis method via spray pyrolysis. Numerous characterization methods, including Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), UV-visible spectroscopy, and high-resolution X-ray diffraction (XRD) techniques have been employed to examine the structures and quality of the NiO nanoparticles thin films. A viable option for the green production of NiO NPs is the use of UV- visible spectroscopy on leaf extracts from fresh leek. Two separate absorption peaks at 303 and 330 nm were obtained in the UV-visible spectra of the leaf extract from fresh Leek leaves. Optimal concentrations (0.02 to 0.045) were determined for the growth of green NiO NPs thin films from the utilized plant, and the impact of growth solution pH (9 to 11.5) on the properties of the NiO NPs thin films was assessed.