The microstructure, charge transport and charge dynamics in blend films of P3HS:PCBM in comparison with P3HT:PCBM in attempt to identify the reasons for the poorer performance in P3HS:PCBM photovoltaic devices. P3HT:PCBM and P3HS:PCBM films were imaged using micro-Raman spectroscopy mapping in order to compare microstructure and phase separation. Both polymer and polymer:PCBM blend solutions were prepared using chlorobenzene and stirred for 24 h to fully dissolve the polymer. P3HT:PCBM and P3HS:PCBM blend films (1:1) were spin-coated onto quartz substrates from warm solutions. Because of low solubility of P3HS P3HS:PCBM films were spin-coated onto substrates that were 80°C. All films were deposited in a clean room with a filtered air environment. Some blend films were thermally annealed at 140°C for 30 mm in a dry nitrogen environment. The result show that fine control of blend film microstructure through the self-organizing properties of the component materials is essential to realize the potential of new organic photovoltaic materials.