We have synthesized graphene nanoparticles (NPs) by the hydrothermal route using carbon tetrachloride organic solvent for various temperatures like 140, 160, and 180 °C in this work. The structural, morphological, optical, and electrical properties of the prepared NPs were studied by advanced techniques such as XRD, SEM with EDX, TEM, AFM, UV, PL, and I-V characteristics. The XRD pattern reveals the hexagonal crystal structure. The SEM image showed textured sheet-like layers which got agglomerated to form fluffy structures. The TEM images recorded single-crystalline nature with spiral spherical shape graphene NPs. The topography images (AFM) reveal the hydrothermal temperature treated influenced the graphene NPs growth. The bandgap of graphene NPS is estimated between 2.02 and 2.32 eV, respectively. All the p-Si/n-Graphene diodes exhibited good rectification nature with less reverse current. The higher temperature achieved minimum n values with higher barrier height. We imply that the p-Si/n-Graphene diode is highly sensitive to synthesize temperature.