Organic photovoltaic cells (OPVs) based on organic semiconductors represent an alternative technology to silicon-based PVs for being lightweight, flexible, and potentially low-cost, as it evolves solution deposition techniques. However, OPVs face several challenges yet, namely lifetimes and efficiency improvements. The maximum power conversion values reported, being ca. 7-8 % [1], are still below the minimum considered necessary for mass production (10 %). In such OPVs, the active layer consists on an electron-donor semiconducting (conjugated) polymer blended with a soluble fullerene, as the electron-acceptor, where donor and acceptor phases are separated at the nanoscale and assembled as an interpenetrating network. Here, we report on OPVs consisting on a columnar-grain layer of cross-linked conjugated polymers, as the electron-donor, covered by a soluble fullerene, as the electron-acceptor (Fig. 1). The polymer layer nanostructuring was performed through co-deposition of an assisting polymer by spin coating [2]. We show that the cells efficiency can be increased upon decreasing the column diameter of the polymer phase, within the nanometer scale. Time-resolved fluorescence studies together with full characterization of the cells indicated that the cells efficiency improvement is mainly due an enhancement of the exciton dissociation (mainly photogenerated in the polymer layer) into charges.