4. Ruthenium-Based Photosensitizers for Dye-Sensitized Solar Cells

Dye-sensitized solar cell (DSSC) is a type of excitonic solar cells with photoanode sensitized by organic molecules, which serve as light harvester. Ruthenium complex-based dyes are a significant class of molecules in the development of DSSCs since 1991. Basically, ruthenium complex is composed of a ruthenium metal center and ancillary ligands. They have been intensively studied because of their excellent photovoltaic properties. In this chapter, we extensively summarize the efforts made to the development of Ru-based dye molecules, such as the approaches to change ancillary ligands of ruthenium complexes and tune the energy levels of the lowest unoccupied molecular orbital and the highest occupied molecular orbital. We also summarize the stability improvement of the dye molecules by introducing hydrophobic ligands. Finally, alternative approaches to expand light response of the Ru dye-sensitized devices including co-sensitization and plasmon-enhanced light harvesting are discussed.