Transition from Anodic Titania Nanotubes to Nanowires: Arising from Nanotube Growth to Application in Dye‐Sensitized Solar Cells

Abstract

Anodic formation of titania nanowires has been interpreted using a bamboo-splitting model; however, a number of phenomena are difficult to explain with this model. Herein, transition from nanotubes to nanowires is investigated by varying the anodizing conditions. The results indicate that the transition requires a large number of hydrogen ions to reduce the passivated area of tube walls, and therefore can be observed only in an intermediate chemical dissolution environment. Accordingly, a model in terms of stretching and splitting is proposed to interpret the transition process. The model provides a basis to suppress the nanowires with surface treatments before anodization and to clear the nanowires with an ultrasonication process after anodization. The nanotube-nanowire transition also arises when the tubes are directly used in dye-sensitized solar cells. Treatment with titanium tetrachloride solution for about 10 h is found to be effective in suppressing the nanowires, and thus improving the photovoltaic properties of the solar cells.

Conformal Growth of Anodic Nanotubes for Dye-Sensitized Solar Cells: Part II. Nonplanar Electrode

“…(3) nanotube diameter also increases with the time; 102 104 (4) nanotubes bundle together under a prolonged anodization duration, 104 due to the formation of nanowires on top of the tubes; 36 (5) a larger growth rate is present for nanotubes grown on the cylindrical substrate as compared to the planar counterpart, 104 consistent with the discussion in Section 2. Such a conformal coating of nanotubes on a metal wire opens up new opportunities for miniature and flexible dyesensitized solar cells.…”

“…For future development, the above issues should be investigated and settled. The cracks induced on the film of long nanotubes are owing to the presence of bundled nanotubes or formation of nanowires under prolonged anodization duration, 36 which are usually along the axial direction of the cylindrical substrate. 101-103 110 111 115 117 This might be related to the termination of tubes at the convex surface of a metal wire, as discussed in Section 2.…”

“…53 165 166 Additionally, other alternative materials of interest with similar nanostructured coatings diversify the pertinent choice, as summarized previously. 36 The tubular electrodes with conformal nanotube coatings can also find interesting application in photovoltaics, which are currently under investigation in our group.…”

Spaced Titania Nanotube Arrays Allow the Construction of an Efficient N‐Doped Hierarchical Structure for Visible‐Light Harvesting

“…This distance is used to decorate the individual NT walls with TiO 2 NPs by using a TiCl 4 hydrolysis approach . In fact, the inter‐tube spacing is sufficiently large that the TiCl 4 treatment can be repeated several times to decorate the NT walls in a layer‐by‐layer approach, thereby maximizing the specific surface area . Figures d and 1 e show SEM images of spaced TiO 2 NTs after eight layers of decoration.…”

Titania Nanostructures for Dye-sensitized Solar Cells

“…TiO 2 nanowires are another important 1D nanostructure that has also attracted a lot of interests regarding an application in DSCs [65][66][67][68][69]. Hydrothermal growth has been reported to be a novel method for synthesis of TiO 2 nanowire array on FTO glass substrate.…”