All-organic chromophores for dye-sensitized solar cells: A theoretical study on aggregation

We report a computational study on the aggregation of organic chromophores used in dye-sensitized solar cells. More specifically, the effects of dimerization on the optical properties are discussed. Ground state properties have been obtained at Density Functional Theory level including dispersion corrections in the case of the dimers, while excited states have been obtained at Time-Dependent Density Functional Theory level. Several stable dimers conformations were obtained, and the influence of the relative inter-monomer angle as well as of substituents has been evidenced. Absorption spectra and excited states topology were investigated for both monomers and dimers. Dimers excited states have been interpreted in the framework of the Kasha exciton theory. Finally, we thoroughly described the photo-induced charge transfer occuring upon excitation. The formation of excitons and the split of electronic density between the two monomers can strongly affect the electronic injection in solar cells devices, since it modifies the nature of the excited states.