Nanowires of wide band gap semiconductors such as zinc oxide and titanium dioxide are emerging as alternatives to mesoporous nanocrystalline films in dye sensitized solar cells (DSSC). In DSSCs assembled using nanoparticles the electrons are transported through the film by hopping through the nanoparticle network. This hopping mechanism slows down the electron transport and limits the film thickness to electron diffusion length. This in turn limits the optical density of the film especially in the infrared where the dye absorption is weak. In nanowires, the hopping transport is replaced by a direct path to the anode so that such devices may show faster transport and higher charge collection efficiencies than nanoparticle DSSCs. While synthesis of single crystal oriented zinc oxide nanowires and polycrystalline titanium dioxide nanowires have been reported, growth of dense arrays of single crystalline titanium dioxide nanowires that are tens of microns long has been elusive. Crystallinity is very important because grain boundaries in polycrystalline materials scatter or trap photogenerated electrons and adversely affect the performance of solar cells. The single-crystallinity and ordered topology could provide direct electrical pathways for photogenerated electrons and enhance the electron transport rate. This in turn may benefit the performance of photocatalytic and photovoltaic devices such as DSSCs. To date, nanowires and nanotubes used to assemble TiO₂-based DSSCs have all been polycrystalline. In this talk, we will describe a simple and environmentally benign method for fabricating oriented single-crystalline anatase TiO₂ nanowire arrays with controlled aspect ratios. Vertically oriented TiO₂ nanowire arrays were grown on titanium foil using a three step synthesis method. The synthesis method relies on the ability to grow single crystal sodium titanate (Na₂Ti₂O₅H₂O) nanowires on titanium foil through a novel alkali hydrothermal growth process. Following growth, the Na₂Ti₂O₅.H₂O nanowires are converted to protonated bititanate (H₂Ti₂O₅.H₂O) nanowires through an ion-exchange reaction without changing their morphology or crystal structure. Finally, the protonated bititanate nanowires are converted to single-crystalline anatase TiO₂ nanowires through a topotactic transformation by calcination. These three sequential steps yield a carpet of 10-50 micron long single crystalline nanowires oriented in the [100] direction and primarily normal to the titanium foil. Preliminary DSSCs using 12 µm thick TiO₂ nanowire films as the photoanode had overall energy conversion efficiencies of 1.4%.