In this study, the synthesis and comprehensive characterization of Fe3O4@SiO2 magnetic nanoparticles (MNPs) immobilized with L-Arginine decorated with nickel (Ni) was achieved, and their ability in solar cell efficiency was evaluated. Fe3O4, Fe3O4@SiO2, Fe3O4@SiO2@L-Arginine and Fe3O4@SiO2@L-Arginine-Ni MNPs were prepared by co-precipitation and sol-gel methods. The structural, morphological, optical and textural properties of the prepared MNPs were clarified by Fourier Transform Infrared Spectroscopy (FTIR), Energy-Dispersive X-Ray (EDX), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Brunauer-Emmett-Teller (BET), Thermal Gravimetric Analysis (TGA) and Ultraviolet-Visible (UV-Vis) analyzes. From the BET data, it is understood that the specific surface area of the prepared Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@L-Arginine MNPs is 60.85, 28.99 and 29.84 m(2)/g, respectively. From the pore size distribution determined by Barrett-Joyner-Halenda (BJH) method, it was understood that the pore radius of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@L-Arginine MNPs were in the range of mesopore and the average pore radius was equal to approximately 11.03, 9.11 and 28.45 nm, respectively. It is assumed that the half pore widths calculated by the density functional theory (DFT) method of the prepared of Fe3O4, Fe3O4@SiO2 and Fe3O4@SiO2@L-Arginine MNPs are 5.58, similar to 0.88, and similar to 17.98 nm, respectively. The energy band gap of the prepared MNPs with spinel structure was determined as approximately 3.10 eV. In addition to the structural, morphological, optical and textural properties, the photovoltaic properties of the prepared MNPs were examined. Au/CuO/Fe3O4@SiO2@L-Arginine-Ni/ZnO/SnO2:F solar cell device was created by using existing Fe3O4@SiO2@L-Arginine-Ni MNPs as buffer layer. The power conversion efficiency (%) of the prepared Fe3O4@SiO2@L-Arginine-Ni MNPs based solar cell device was calculated as 1.84 %. This numerical result shows that the prepared Fe3O4@SiO2@L-Arginine-Ni MNPs can be used as a promising buffer layer in a solar structure.