Nanoparticle Layers Transformed from Ordered TiO 2 Nanotube Arrays and Dye-Sensitized Solar Cells

Transformation of titanium dioxide (TiO2) nanotubes (NTs) to truncated bipyramidal shape nanoparticles (NPs) with a large fraction of photo-catalytically active {001} facet surface was observed after thermal annealing TiO2 ordered nanotube arrays in fluorine ambient. Size of the formed nanoparticles depended on fluorine concentration and can be controlled from 20 nm to 350 nm. The crystal and optical properties of nanoparticle layers are superior to those of nanotube arrays, which are also annealed but without geometrical transformation. Using nanoparticle layers formed by this method we have fabricated dye-sensitized solar cells (DSSCs) with different size NPs in the range 35-350 nm. The dependence of solar cell performance on NP size is discussed.