Titanium Dioxide Nanotubes for Dye-Sensitized Solar Cells: Improving Efficiencies

16-CNT Dye Solar Cells figure1Titanium dioxide (TiO2) has distinct properties. It is a semiconductor that is photocatalytic, non-toxic, biocompatible and easy to fabricate. This makes it attractive for a wide range of applications such as sensors, human implants and dye-sensitized solar cells (DSSCs). In DSSCs, the one-dimensional (1D) structure of TiO2 nanotubes provides a direct pathway for electrons up to the collecting electrode. It also has fewer trapping sites than conventional structures. Highly ordered TiO2 nanotubes are required for more efficient devices and, reporting in Nanotechnology, researchers have investigated the factors influencing this.

Here, highly ordered TiO2 nanotube arrays are synthesized using the electrochemical anodization of Ti foils subjected to an electropolishing pre-treatment. The researchers unveil the decisive role played by the electropolishing of the Ti foil on the anodic TiO2 nanotubes to obtain a hexagonal closed-packed array distribution.

Surface ‘waviness’

Besides the usual advantages, such as size control, the electropolishing surface “waviness” improves the organization of anodic oxide nanopores or nanotubes. This new overriding application of electropolishing creates nanopatterns in the surface of titanium. This works as a pre-pattern prior to the anodization and ultimately leads to highly ordered oxide nanostructures.

Improving organization

A multidisciplinary team, which includes researchers from the Universidade do Porto in Portugal, studied the prior-anodization Ti surface topography with different electropolishing potentials. Optimized Ti surfaces with lower roughness and topographic nanopatterning are obtained. These lead to fast growth rates of nanotubes with higher organization (ideal hexagonal closed-packed array distribution).

The researchers found that the Ti surface roughness plays an important role in the onset of pore nucleation in enhancing the local focusing effect of the electrical field. Additionally, the electropolishing induces periodic dimple structures on the metal surface. This leads to a preferential ordered pore nucleation, offering an organization improvement of the anodic oxide NTs.

More information about this research can be found in the journal Nanotechnology 25 485301 (IOPselect article).

Further reading

Improving the performance of dye-sensitized solar cells at larger cell sizes (Jan 2013)
Nb-doped titania electrode helps make good solar cell (Oct 2013)
Patterning bumpy surfaces (July 2014)

About the author

Arlete Apolinário is a PhD student at the IFIMUP and IN- Institute of Nanoscience and Nanotechnology, from Universidade do Porto in Portugal. With a background in materials physics, her current research interests focus on nanostructured semiconductors (titania and hematite nanotubes) synthesis for photoelectrochemical and dye-sensitized solar cells.

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