Synthesis of Morphology-Controlled Titania Nanocrystals and Application for Dye-Sensitized Solar Cells

Development of renewable energy resources in the near future is an urgent issue. One attractive strategy is the development of dye-sensitized solar cells (DSSCs); they are extremely promising, because they are made of low-cost materials and do not need elaborate apparatus to manufacture. Titania is the most promising material for the electrode of DSSCs, and then morphological control and carrier transport optimization are the key properties needed in titanium oxide materials for DSSCs. We review the formation procedures and characteristics of titanium oxide nanocrystalline products, which exhibit various morphological shapes in nanometer scale, i. e., nanotubes, nanorods, nanowires and nanosheets, and their arrays. We also present new findings in our laboratory on the formation of titania nanorods and network structures of single-crystal-like titania nanowires as well as their application for DSSCs. In order to evaluate the electrical properties of DSSCs with electrodes composed of various nanoscale titania materials, measurement procedures for electron transport processes in DSSCs are also reviewed, together with our results in electrochemical impedance spectroscopy to determine various parameters concerning about electron transport.