Probing the regeneration process of triphenylamine-based organic dyes in dye-sensitized solar cells

The regeneration processes of triphenylamine (TPA)-based dyes with cobalt redox mediator in dye-sensitized solar cells (DSSCs) have been investigated using density functional theory combined with the Marcus theory of electron transfer. Our results show that with the extension or rigidification of the oligothiophene conjugation linker the absorption spectra of TPA dyes exhibit observable red-shift in the maximum absorbance that favors light-harvesting, while the electron transfer rates for dye regeneration decrease in some degrees due to the increased activation free energies and the reduced electronic coupling energies which hampers the dye regeneration. Importantly, the undesirable influences on dye regeneration by extending the linker moiety are more significant than that by the way of rigidification. Thus, the rigidification is a better choice than the extension of the conjugated moiety for the design of D-π-A type dyes based on the properties of light-harvesting and the kinetics of dye regeneration.