Graphene/Ag nanoparticles (GAg) were fabricated via a facile method, employing graphite oxide as a precursor of graphene sheet (GNS), AgNO₃ as a precursor of Ag nanoparticles, and sodium citrate as a reducing and stabilizing agent. We synthesized three kinds of GAg as GAg-1, GAg-2 and GAg-3. We introduced high electron mobility GAg into the active layer of polymer solar cell. The cell structure was ITO/PEDOT:PSS/P3HT:PCBM:GAg/Ca/Al. The weight ratio of P3HT:PCBM:GAg of active layer is 1:1:0.01. We study the effect of GAg addition on the photovoltaic performance. We use the UV-Vis, SPM, FE-SEM and solar simulator to measure the absorbance, roughness, surface morphology, and power conversion efficiency (PCE), respectively. From these results, we found that the fill factor (FF) and PCE of the cells with GNS or GAg are always higher than those of cell without GNS or GAg. The cell with GAg-2 had the highest short circuit current density (J_sc) of 8.56 mA/cm2, an increase of 20.2%, the highest fill factor (FF) of 0.56, an increase of 14.3% and the highest PCE of 2.78%. This is a 24.7% increase in efficiency compared to the cell without GNS or GAg. These improvements were due to the high carrier mobility of grapheme.