Enhanced efficiency of dye-sensitized solar cells through TiCl ₄-treated, nanoporous-layer-covered TiO₂ nanotube arrays

TiCl₄-treated, nanoporous-layer-covered TiO₂ (Type II) nanotube arrays are fabricated through a two-step anodization process followed by treatment with TiCl₄. A dye-sensitized solar cell (DSSC) with TiCl₄-treated, nanoporous-layer-covered Type II TiO₂ nanotubes is compared with other DSSCs based on untreated Type II and both untreated and TiCl₄-treated, conventional TiO₂ (Type I) nanotube arrays. The TiCl₄ surface treatment's effects on dye adsorption, charge transport, and electron lifetime are dependent on the morphologies of the TiO₂ nanotubes. The TiCl₄-treated Type I nanotubes allow higher dye adsorption, whilst the TiCl₄-treated Type II nanotubes provide much faster electron transport and enhanced electron lifetime. This is because there are fewer defect traps in the nanostructure well-aligned without bundling, which contributes to the significantly improved cell performance over the DSSC with the TiCl₄-treated Type I nanotubes.