New materials and structures have been developed for efficient organic solar cells, dye-sensitized solar cells (DCSs) and organic thin-film solar cells (OPVs). Some strategies for achieving high photon-to-electricity conversion efficiency in these solar cells are discussed, focusing on nanostructured materials. In the case of DSCs, unlike TiO2 nanoparticles, TiO2 nanotubes with suitable dimensions are expected to work as efficient light scatterers as well as to give large surface areas for charge separation. A strategy for designing triarylamine-functionalized ruthenium dyes, which display the high efficiency, is also proposed. Furthermore, OPVs based on donor/acceptor (D/A) block copolymers are discussed, focusing on the phase separation of donor and acceptor segments and their domain sizes.