Highly efficient dye-sensitized solar cells were produced using single-crystalline TiO2 nanotubes as a thin-film semiconductor because of the very high electron transfer through single-crystalline TiO2 nanotubes when compared to that through nanoporous TiO2 films composed of nanoparticles. The dye-sensitized solar cells with single-crystalline TiO2 nanotubes showed more than double the short-circuit current density than those made of titania nanoparticles Degussa P-25 in the thin-film thickness region. Titania nanotubes were synthesized using molecular assemblies composed of surfactant molecules, i.e., laurylamine hydrochloride, and titanium alkoxide, i.e., tetraisopropylorthotitanate modified with acetylacetone, as a template. They have outer and inner diameters of about 10 and 5 nm, respectively, a length in the range from 30 nm to several hundred nanometers, and have a single-crystalline structure of anatase, as confirmed on lattice images observed by high-resolution transmission electron microscopy. The light to electricity conversion of the titania nanotube cells was around 5%. They also showed the highest photocatalytic activity when compared to the commercially available nanocrystalline titania. (C) 2003 The Electrochemical Society.