Organic solar cell (OSC) materials have recently gained rich attention due to capable of efficient power conversion, cost-effective, mechanically flexible and light weight solar cells. At the same time further materials developments for high performance will be necessary for commercial production of organic photovoltaics. The increase of efficiency has resulted from the low band gab materials, combination of polymer: fullerene and presence of blend micro structure. In this regard, the authors have achieved an efficient polymer solar cells based on Poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno[3,4-b]thiophenediyl](PTB7) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as donor and acceptor respectively. The photocurrent active layers were fabricated by spray coating technique which enables large area, low cost solar cells. A systematic analysis of PTB7:PC71BM devices carried out with TiOx electron transport layer, Chlorobenzene (CB) and 1,8 Diiodooctane (DIO) solvents. Optical and surface characterization analysis carried out by UV-visible and AFM techniques respectively. From the J-V characteristics, the device prepared with CB+DIO mixture solvents and TiOx layer exhibits the best power conversion efficiency of 4.90%. It shows the device efficiency is one order of magnitude higher compared to that achieved with a TiOx electron transport layer and without DIO solvent. The obtained results shows that DIO cosolvent induced changes in active layer morphology down to nano scale range and the TiOx layer decrease the resistance between the active layer and electrode material.