Abstarct: Solar cells are devices for converting sunlight into electricity. Solar cells, especially organic solar cells, have attracted a lot of attention in recent years due to their flexibility and low manufacturing cost. In this study, we studied the polymer solar cell, which is one of the types of organic solar cells. To improve the polymer solar cell, we used multilxayer graphene material as a cathode with aluminum due to its high absorption and high mobility of charge carriers. The structure of Al / Graphene / P3HT: PCBM / Au is simulated using Silvaco Tcad software. In many organic solar cells, ITO is used as a photodiode and in the reverse structure as a cathode due to its high transparency and therefore efficiency. Since the preparation of ITO requires a high cost, we have removed it in the structure and used graphene material instead. Final simulations has been performed on Al/Graphene/P3HT:PCBM/Spiro-OmextaD/structure and baxsed on them photovoltaic parameters of the solar cell were obtained per 10 nm graphene laxyer as Voc=1.2V, Jsc=9.46mA/cm2, and FF=80%. Power conversion efficiency of the proposed structure is 9.08%.