In this paper, we present a simulation study for a newly prepared organic solar cell, based on a composite of poly (2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylenevinylene (MEH-PPV) with [6, 6]-phenyl C60 butyric acid methyl ester (PCBM). Photo-current density vs. voltage (J–V) characteristics, for the cell, which were experimentally studied earlier, have been revisited here. The results indicated that the conduction mechanism in the organic solar cell is strongly influenced by the excitonic diffusion. Sound correlation, between theoretical and experimental photo-current density vs. voltage (J–V) plots, has been achieved. Moreover, the simulation clearly demonstrates that the performance of the tested device can be described, with sound accuracy, by a two-diode-equivalent model.