Electronic and optical properties of the triphenylamine-based organic dye sensitized TiO2 semiconductor: insight from first principles calculations.

Plausible mechanisms of the ultrafast electron injection and the significant dependence of the power conversion efficiency on the anchor group for the triphenylamine-based dye-sensitized TiO2 solar cells have been explored by the density functional calculations. Calculations show that the ultrafast charge recombination on the surface trap state of the dye-sensitized TiO2 system can be ascribed to the lack of electron density on the carboxyl group of the A3 dye with the rhodanine group anchor. Predicted electronic and optical properties of the A1-3-adsorbed TiO2 system reveal that the direct electron injection arises from the electronic excitation from HOMO-1 of the dye to the conduction band bottom of TiO2. On the basis of the calculations, the electron density distributions of related frontier orbitals and energy bands of dyes and their adsorbed systems have been discussed, which play an important role in electron injection and charge recombination.