Nanocrystalline anatase TiO₂ derived from a titanate-directed route for dye-sensitized solar cells

TiO₂ nanoparticles used in numerous applications are generally prepared from the sol-gel method. Because of the competitive, rather than exclusive, formation of the three TiO₂ polymorphs, anatase, brookite and rutile, in the sol-gel synthesis, phase-pure nanoparticles can hardly be obtained. The present work demonstrates a unique route, alternative to the conventional sol-gel method, to prepare high-purity anatase TiO₂ colloids, which can be deposited as electrodes for dye-sensitized solar cells (DSSCs) to facilitate electron transport and avoid charge recombination. In this developed route, a titanate with its TiO₆ octahedra arranged in a zigzag configuration, which is also a characteristic feature of anatase TiO₂, is produced as an intermediate. Raman analysis shows that a phase-pure anatase TiO₂ colloid is prepared from the developed route, while the TiO₂ derived from the sol-gel at the same temperature is predominantly composed of anatase with the presence of a minute amount of rutile and brookite. Because of the high-purity in anatase phase, the TiO₂ colloid derived from the titanate-directed route is shown to constitute a mesoporous film exhibiting high performance in a dye-sensitized solar cell.