Polymer blends are thermodynamically unstable towards phase separation. This principle has been used to prepare structured materials, in particular films made of conjugated polymers. In this communication we report on studies on the phase separation between polystyrene, used as an assistant polymer, and cross-linkable conjugated polymers derived from polyfluorenes. In particular, we have used this strategy to fabricate insoluble films with nanostructured surfaces made of a cross-linkable polymer. These films were afterwards covered with PCBM from solution to obtain nanostructured donor/acceptor interfaces for photovoltaic cells, PVs. We compare the power conversion efficiency of cells prepared with three different interfacial motives and find that PCE increases upon decrease of interfacial structures dimensions. These cells perform better than similar PVs made with planar interfaces but their PCE values are below those of similar bulk heterojunctions PVs, which we attribute to the still large columns size (ca. 200 nm in diameter). In view of the easy processing and possibilities to be extended towards large area devices, we consider this is an approach that may contribute to improve organic solar cells performance.