Nanostructured materials for efficient solar energy conversion

Substituent effects of porphyrins and phthalocyanines in dye-sensitized solar cells have been examined to elucidate the close relationship between the molecular structure and the photovoltaic properties toward the improvement of cell performances. Introduction of bulky mesityl groups into the phthalocyanine core was found to reduce the dye aggregation considerably, leading to the small effect of coadsorbent (chenodeoxycholic acid (CDCA)) on the photovoltaic properties. Little effect of CDCA on the photovoltaic properties of a cell with phthalocyanine diacid indicates that the phthalocyanine molecules bind to the TiO₂ surface irregularly because of the complex binding state arising from the multiple binding and a complicated mixture of the isomers. The results of other nanostructured materials (i.e., porphyrin, fullerene, carbon nanotube) for efficient solar energy conversion are also presented.