The performance of dye-sensitized solar cells (DSSCs) depends significantly on the adsorption geometry of the dye on the semiconductor surface. In turn, the stability and geometry of the adsorbed molecules is influenced by the chemical environment at the electrolyte/dye/TiO 2 interface. To gain insight into the effect of the solvent on the adsorption geometries and electronic properties of dye-sensitized TiO 2 interfaces, we carried out first-principles calculations on organic dyes and solvent (water or acetonitrile) molecules coadsorbed on the (101) surface of anatase TiO 2. Solvent molecules introduce important modifications on the dye adsorption geometry with respect to the geometry calculated in vacuo. In particular, the bonding distance of the dye from the Ti anchoring atoms increases, the adsorption energy decreases, and the two C-O bonds in the carboxylic moieties become more symmetric than in vacuo. Moreover, the adsorbed solvent induces the deprotonation of the dye due to the changing the acid/base properties of the system. Analysis of the electronic structure for the dye-sensitized TiO 2 structures in the presence of coadsorbed solvent molecules shows an upward shift in the TiO 2 conduction band of 0.2 to 0.5 eV (0.5 to 0.8 eV) in water (acetonitrile). A similar shift is calculated for a solvent monolayer on unsensitized TiO 2. The overall picture extracted from our calculations is consistent with an upshift of the conduction band in acetonitrile (2.04 eV vs SCE) relative to water (0.82 eV vs SCE, pH 7), as reported in previous studies on TiO 2 flatband potential (Redmond, G.; Fitzmaurice, D. J. Phys. Chem.1993, 97, 1426-1430) and suggests a relevant role of the solvent in determining the dye-semiconductor interaction and electronic coupling.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films