To model the active layer in the hetero-junction solar cells, the C60, C70, PC60BM, PCBDAN fullerenes as acceptor, and (OS)n=1) oligoselenophenes as donor were considered. The (OS)n=14/C60, (OS)n=14/C70, (OS)n=14/PC60BM, and (OS)n=14/PCBDAN blends as a model of the active layer in the BHJ solar cell were chosen, and the optoelectronic properties were studied. The calculated efficiency of these complexes based on the Scharber diagram is 8%, 8.2%, 9.3%, and 9.7%, respectively. These results indicate that the (OS)n=14/PCBDAN blend is a favorable candidate as solar cell than that of the other blends. In order to investigate the effect of the chain length of oligomers on the solar cell properties, the optoelectronic properties of (OS)n=12/C60 blend was also studied. The electronic and optical properties and the calculated efficiency values of (OS)n=12/C60 and (OS)n=14/C60 (7.7% and 8% respectively) show that the (OS)n=14/C60 complex is more suitable candidate than the (OS)n=12/C60 complex for modeling the active layer in the BHJ solar cells.