New [60] and [70]fullerene homo- and heterodimers absorbing in the visible region have been synthesized and fully characterized. In order to increase the solubility and processability of the new fullerene dimers, different alkyl chains have been used which has allowed the determination of the influence of the solubilizing alkyl groups on the photovoltaic performance. Atomic force microscopy experiments carried out on blends of these dimers and P3HT evidenced the formation of large aggregates, which significantly influence the photovoltaic efficiency.