Thermodynamic Control over the Competitive Anchoring of N719 Dye on Nanocrystalline TiO2 for Improving Photoinduced Electron Generation

TiO2 electrodes, sensitized with the N719 dye at high immersion temperatures during the sensitization process, were found to have large fractions of weakly bound N719 on the electrode surface, which resulted in dye aggregation and decreased device longevity. These disadvantages were ameliorated using a low-temperature stearic acid (SA)-assisted anchoring method described here. The activation energy (Delta E-NS(double dagger)) and relative fraction of strongly bound N719 were twice as large as the respective values obtained without the use of SA. Slowing of adsorption, both by thermal means and through SA-mediated processes, effectively controlled the binding mode of N719 on the surface of TiO2. The resulting sensitized electrodes displayed enhanced device longevity and improved generation of photoinduced electrons.