Creation of Nano-Molecular Assemblies Using Intermolecular Interactions and its Photofunction

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Novel organic solar cells have been prepared using quaternary self-organization of porphyrin (donor) and fullerene (acceptor) units by clusterization with gold nanoparticles on nanostructured SnO_2 electrodes. First, porphyrin-alkanethiolate monolayer-protected gold nanoparticles (H_2PC nMPP : nis the number of methylene groups in the spacer) are prepared (1st step) starting from the primary component (porphyrin-alkanethiol). These porphyrin-modified gold nanoparticles form complexes with fullerene molecules (2nd step), and they are clusterized in acetonitrile/toluene mixed solvent (3^<rd> step). The highly colored composite clusters can then be assembled as threedimensional arrays onto nanostructured SnO_2 films to afford the ITO/SnO_2/(H_2PC nMPP+C_<60>)_m electrode using an electrophoretic deposition method (4^<th> step). The film of the composite clusters with gold nanoparticle exhibits an incident photon-to-photocurrent efficiency (IPCE) as high as 54% and broad photocurrent action spectra (up to 1000 nm). The power conversion efficiency of the ITO/SnO_2/(H_2PC15MPP+C_<60>)_m composite electrode reaches as high as 1.5%, which is 45 times higher than that of the reference system consisting of the both single components of porphyrin and fullerene.