Role of One-Dimensional Ribbonlike Nanostructures in Dye-Sensitized TiO2-Based Solar Cells

In dye-sensitized solar cells, there is a competition between transport of electrons through the porous semiconductor electrode toward the conducting substrate and back-reaction of electrons to recombination with I-3(-) ions on the semiconductor electrolyte interface, which determines the charge collection efficiency and is strongly influenced by the electronic site distribution in intraband and geometrical structure of the semiconductors. Herein, we systematically analyze the electrochemical parameters of TiO2 nanoribbon- and nanoparticle-based electrodes by electrochemical impedance spectroscopy. The results show that the intrinsic one-dimensional crystalline structure of TiO2 nanoribbons can promote formation of a space charge layer on the surface of the semiconductor, which effectively blocks the recombination of electrons with I-3(-) ions in the semiconductor electrolyte interface, resulting in an increase of electron lifetime and a higher cell voltage. Furthermore, the boundaryless structure of the TiO2 nanoribbons provides efficient channels for electron transport and therefore increases electron diffusion length. The combination of TiO2 nanoparticle-based electrode with TiO2 nanoribbons can significantly improve energy conversion efficiency of similar to 60%. These data provide a basic understanding of the role of TiO2 geometrical structure in solar energy conversion.