TiCl4-treated, nanoporous-layer-covered TiO2 (Type II) nanotube arrays are fabricated through a two-step anodization process followed by treatment with TiCl4. A dye-sensitized solar cell (DSSC) with TiCl4-treated, nanoporous-layer-covered Type II TiO2 nanotubes is compared with other DSSCs based on untreated Type II and both untreated and TiCl4-treated, conventional TiO2 (Type I) nanotube arrays. The TiCl4 surface treatment's effects on dye adsorption, charge transport, and electron lifetime are dependent on the morphologies of the TiO2 nanotubes. The TiCl4-treated Type I nanotubes allow higher dye adsorption, whilst the TiCl4-treated Type II nanotubes provide much faster electron transport and enhanced electron lifetime. This is because there are fewer defect traps in the nanostructure well-aligned without bundling, which contributes to the significantly improved cell performance over the DSSC with the TiCl4-treated Type I nanotubes. (C) 2011 Elsevier B.V. All rights reserved.