The power conversion efficiency (PCE) of single junction organic solar cells has increased significantly during the last decade to 9-10%, now approaching the threshold considered necessary to commercialize the technology. During this period, the structural diversity of semiconducting donor polymers for solar cells has increased dramatically, enabling accelerated development of bulk heterojunction (BHJ) organic solar cells based on polymer donor materials and molecular fullerene derivatives. One aspect of this presentation is to illustrate one molecular design strategy used to optimise a new class of donor polymer. However, the development of electron accepting materials that lead to BHJs with high PCE has been significantly slower. The most commonly used n-type acceptors to date remain [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) and its slightly larger counterpart PC71BM. These fullerene acceptors have significant limitations including weak absorption and poor tunability of absorption over the range of intense regions of the solar spectrum; morphological instability in thin film blends over time; high synthetic costs and limited scope for synthetic control over electronic and structural properties. For these reasons, we have developed new, synthetically simple electron acceptor materials, based on rhodanine end groups, which have high lying LUMO energy levels and much larger absorption coefficients that fullerenes. In BHJ devices with P3HT donor polymer, the rhodanine molecules were demonstrated to outperform the fullerenes. Our synthetic strategy was to make “dumbbell” shaped dimeric fullerenes where the fullerenes are linked via an alkyl bridge between the ester functional group on PCBM. This was shown to inhibit large scale crystallisation.