Fabrication of dye-sensitized solar cells using a both-ends-opened TiO₂ nanotube/nanoparticle hetero-nanostructure

We fabricated a hetero-structure photoanode with both-ends-opened TiO₂ nanotubes and TiO₂ nanoparticles for dye-sensitized solar cells (DSSCs). Two-step anodization and selective etching process were used to obtain the both-ends-opened TiO₂ nanotubes. A heat treatment was employed to obtain anatase crystal-structured nanotubes. The effect of the both-ends-opened TiO₂ nanotubes on the photoelectric conversion efficiency (PCE) of the DSSCs was evaluated by positioning the TiO₂ nanotubes on TiO₂ nanoparticle layers and by sandwiching them between the TiO₂ nanoparticles. It is suggested that both-ends-opened TiO₂ nanotubes serve as incident light scattering layers that lead to superior light harvesting efficiency of DSSCs. This increases the electron lifetime and results in the recycling of more light by dye molecules, thus increasing the photocurrent density. Consequently, a high PCE of 7.74% was obtained when the TiO₂ nanotubes were placed on the TiO₂ nanoparticles and a PCE of 8.56% was obtained when the TiO₂ nanotubes were placed between the TiO₂ nanoparticles.