New materials and structures have been developed for efficient organic solar cells such as dye-sensitized solar cells (DCSs) and organic thin-film solar cells (OPVs). In this paper, the authors discuss various strategies for achieving high conversion efficiency in organic solar cells, focusing on nanostructured materials. In the case of DSCs, TiO(2) nanotubes with suitable dimensions are expected to function as efficient charge transport layers because the rate constant of back electron transfer in a TiO(2) nanotube layer is smaller than that in a nanoparticule layer. A new derivative of triarylamine-functionalized ruthenium dyes is also synthesized, aimed at the efficient electron transfer from the dye to TiO(2). Furthermore, OPVs based on donor/acceptor (D/A) block copolymers are discussed, focusing on the exciton binding energy of donor and acceptor segments.