Exploring the regeneration process of ruthenium(II) dyes by cobalt mediator in dye-sensitized solar cells from first-principle calculations

The regeneration of ruthenium(II) dyes by cobalt redox mediator in dye-sensitized solar cells (DSSCs) has been investigated using density functional theory combined with the Marcus theory of electron transfer. Our results show that the regeneration reaction rates gradually increase with the growth of the dye protonation degree. By comparing the natures of protonated and deprotonated states, we reveal that design of charge-neutral dye is the best choice to obtain fast dye regeneration and suppress the undesired recombination reaction of the injected photoelectrons. Furthermore, the dye-cobalt mediator associated configuration is found to influence the regeneration reaction rates remarkably by varying the electronic coupling energy. The electronic coupling energy largely depends on the frontier orbitals distribution of the reactants, so the matching of the electronic configuration of the dyes and the cobalt mediators should be judiciously conceived.