Transparent electrodes of ordered opened-end TiO2-nanotube arrays for highly efficient dye-sensitized solar cells

We introduce a version of a dye-sensitized solar cell (DSSC), in which the transparent electrode comprises an opened-end TiO2-nanotube (TiNT) film oriented perpendicular to the fluorine-doped tin oxide (FTO) conductive glass. This electrode is fabricated using a facile process involving flaking the anodic TiNT film off the Ti-metal substrate to open its closed bottom and strongly adhering it onto FTO glass by a nanocrystalline TiO2 (NP-TiO2) thin underlayer. Apart from the enhanced light-harvesting and electron-collecting efficiencies, the use of opened-end TiNT film allows the redox electrolyte (iodide, I- and triiodide, I-3(-)) easy access to the NP-TiO2 underlayer. As compared to the closed-end TiNT-based DSSC, the opened-end TiNT-based device exhibited an increase in one-sun efficiency from 5.3% to 9.1%, corresponding to 70% enhancement.