Supramolecular photovoltaic cells based on composite molecular nanoclusters: Dendritic porphyrin and C ₆₀, porphyrin dimer and C ₆₀, and porphyrin-C ₆₀ dyad

Novel organic solar cells have been prepared using molecular clusters of porphyrin dendrimer (donor) and fullerene (acceptor) dye units assembled on SnO ₂ electrodes. The molecular clusters of porphyrin with dendritic structure and fullerene exhibit controlled size and shape in contrast with the reference systems (a porphyrin dimer and a porphyrin-fullerene dyad) without dendritic structure in TEM images, which show rather irregular and smaller clusters. The composite molecular nanoclusters of dendritic porphyrin and fullerene prepared in acetonitrile/toluene mixed solvent absorb light over entire spectrum of visible light. The comparison of photoelectrochemical properties of composite molecular cluster of porphyrin and fullerene with that of molecular cluster of porphyrin-C ₆₀ dyad with covalent linkage shows the importance of interpenetrating structure in each network to transport hole and electron efficiently. Furthermore, organic photovoltaic cells using clusters of supramolecular complexes of V-shaped porphyrin dimer and porphyrin dendrimers with fullerene exhibit remarkable enhancement in the photoelectrochemical performance as well as broader photoresponse in the visible and near-infrared regions as compared with the reference system. This clearly indicates that the π-π interaction between porphyrins and fullerenes in the supramolecular clusters plays an important role in improving the light energy conversion efficiency.