Open-ended TiO ₂ nanotubes formed by two-step anodization and their application in dye-sensitized solar cells

We demonstrate a simple method to fabricate open-ended TiO ₂ nanotube (NT) based dye-sensitized solar cells (DSSCs), where the NTs are attached to either TiO ₂ nanorods (NRs) grown on fluorine-doped tin oxide (FTO) or FTO directly by nanoparticles (NPs). A completely hole-through TiO ₂ NT layer is fabricated via a two-step anodization with heat treatment immediately after the first anodization. DSSCs with the open-ended NTs show better photovoltaic performance than those with close-ended NTs, due to the enhanced charge transport in the open-ended structure. Under optimum conditions, DSSCs fabricated with the open-ended NT layer exhibit a short circuit current density (J _sc) of 19.10 mA cm ^-2, an open circuit voltage (V _oc) of 0.68 V, a fill factor (FF) of 0.49, and a power conversion efficiency (eff) of 6.3%.