Core substituted perylene diimides are promising n-type semiconductor materials for organic photovoltaic applications. We have prepared three Donor-Acceptor-Donor perylene diimide molecules, substituted in bay positions with bithiophene, spirobifluorene and bithiophene spirobifluorene groups. These molecules were tested as electron acceptors, in blend with P3HT as donor material, in bulk heterojunction solar cells. The active layers of these devices were optimized by thermal treatment or by the presence of additives and the photovoltaic characteristics were measured. The photovoltaic performances of the three perylene diimides were studied and discussed through absorption and emission spectroscopy characterization, atomic force microscopy morphology study and charge-carrier transport measurements.