Carbon nanotubes are envisaged to improve the overall efficiency and to enhance the charge separation and/or transport of conjugated polymer-fullerene derivatives blends. In this work, we investigated the effect of the incorporation of semiconducting single walled carbon nanotubes (6,5) (SWNTs (6,5)) into P3HT:PC70BM solar cells. In particular, we examined how the device performance was influenced by the quality of nanotube dispersions, the choice of dispersing solvent and of the sorting polymer. The blade-coating deposition technique was employed for large-scale applications. The SWNTs (6,5) were deposited from different solvents in two configurations: i) before or after active layer deposition as films, or ii) mixed with the P3HT:PC70BM blend in a bulk configuration. (6,5) SWNTs were processed, on one hand, with a low-cost approach consisting of sonicating the as-purchased nanotubes in either DMF or ODCB followed by centrifugation, in order to separate the remaining bundles and impurities. On the other hand, conjugated polymers were added during the sonication in order to sort the nanotubes selectively for a higher purity enriched dispersion free of metallic species. Both inverted and conventional geometries were studied. Regardless of the device geometry, it was found that the deposition of SWNTs (6,5) close to the hole transport layer (HTL) (PEDOT:PSS in our case) resulted in an enhanced device performance. In contrast, a decreased performance was observed when nanotubes were deposited close to the electron transport layer. This indicates that SWNTs can enhance the transport of holes, possibly due to their p-type charge transport behavior. It is also likely that this difference in the device performance is affected by the nanotubes position relative to the active layer due to differences in the morphology, therefore affecting the degree of interaction between the P3HT:PC70BM and the SWNT layer. It seems that there is a stronger interaction between P3HT:PC70BM blend and the SWNTs when the latter are placed close to the HTL. However, in the case of the bulk configuration, the device performance decreased with increasing concentration of SWNTs (6,5) in the blends, more likely due to increased charge-recombination in addition to the presence of large aggregates of nanotubes. To gain further insight into the morphology and the charge-transfer processes of the active layer of these devices, tapping-mode atomic force microscopy and femtosecond transient absorption spectroscopy studies were also performed. Our work highlights the potential of semiconducting SWNTs for improving the performance of organic solar cells.