**Table 1.**

devices at a maximum wavelength reached more than 70% for P3HT:PC61BM solar cells, compared to ~50% for MDMOPPV: PC61BM solar cells [15]. Because of the semicrystalline nature of P3HT spin-cast films, it has among the highest reported field-effect transistor mobilities for a conjugated polymer. The morphology and the mobility of pure rr-P3HT and blended rr-P3HT: PCBM films are highly dependent on casting conditions [16, 17].

The flexible side chain of the P3HT molecule introduces a good solubility in organic solvents in spite of its kind as stiff polymers. The long and narrow fibrils which are produced by P3HT crystalizes are from a network that is able to create a good percolation paths for the charge carriers' transportation. This leads to high carrier mobility. Differing from the P3HT, PCBM is a derivative of fullerene; it has a high electron affinity which makes it a qualified electron acceptor material in the organic thin film solar cells as shown in **Table 1** [18].
