An atomistic picture of the regeneration process in dye sensitized solar cells

A highly efficient mechanism for the regeneration of the cis-bis(isothiocyanato) bis(2,2'-bipyridyl-4,4'-dicarboxylato)-ruthenium (II) sensitizing dye (N3) by I- in acetonitrile has been identified by using molecular dynamics simulation based on density functional theory. Barrier-free complex formation of the oxidized dye with both I- and I-2(-), and facile dissociation of I-2(-) and I-3(-) from the reduced dye are key steps in this process. In situ vibrational spectroscopy confirms the reversible binding of I-2 to the thiocyanate group. Additionally, simulations of the electrolyte near the interface suggest that acetonitrile is able to cover the (101) surface of anatase with a passivating layer that inhibits direct contact of the redox mediator with the oxide, and that the solvent structure specifically enhances the concentration of I- at a distance which further favors rapid dye regeneration.