Effect of Ligand Carboxylation on Adsorption and Photosensitization in Ru(II)-Complex Dye-Sensitized Nanocrystalline TiO 2 Solar Cell

The kinetics of dye adsorption onto a mesoporous TiO 2 film is compared between Ru(II) complex dyes with and without carboxy groups in the bipyridyl ligand, by diffuse reflectance spectroscopy at room temperature. Both dyes show adsorption saturation, and the dye without carboxy groups simply obeys the Langmuir isotherm equation. The dye with carboxy groups exhibits the same kinetics as the dye without carboxy groups in the period up to 20 min. However, in contrast to the latter, it increases its adsorption rate after this time, suggesting a change of the adsorption mode from physisorption to chemisorption. The carboxy group in the dye-sensitized solar cell is assumed to play a role in the chemical modification of the TiO 2 surface via a two-step adsorption from physisorption to chemisorption.