In recent years, Solar cells, as a competitive energy source with fossil fuel, have appeared. Researchers have paid a great deal of attention to research and development of organic solar cells. This article leading a breakthrough of over 10% power conversion efficiency.Though impressive, further development is required to ensure a bright industrial future organic photovoltaic. Relatively narrow spectral overlap of organic polymer absorption bands within the solar spectrum is one of the major limitation of organic solar cells. Among different strategies that are in progress to tackle this restriction, the novel concept of low band gap materials is a promising candidate to extend the absorption spectra of sun light and to enhance light harvesting in bulk-heterojunction solar cells. The potential advantages of polymer solar cells are numerous including flexibility , processability , low material cost , independence on scarce resources and large-area application.The flexibility as an advantage, is a feature allowing the solar cells to be incorporated into application that solar panels can be rolled out onto a roof or other surface are one option. Processability is another major selling point of polymer solar cells. Both first and second generation solar cells depend on vacuum deposition methods requiring massive amount of energy; with polymer based organic solar cells, on the other hand, layers are processed from solution and complete solution processed cells are an possibility. This allows for upscaling the production and thus reducing the cost per area of polymer solar cells. Many second generation solar cells utilize materials that are scarce in nature. Also with polymer solar cells this can be avoided.