Interaction between disulfide/thiolate mediators and ruthenium complex in dye-sensitized solar cells

The intermolecular interactions of thiolate anions and disulfide molecules as disulfide/thiolate (T-2/T-, S-2/S-) redox couples with a Ru bipyridyl complex (Z907) are investigated using density functional theory. T and S are 1-methyl-1H-tetrazole-5-thiolate and 2-methyl-5-trifluoromethyl-2H-1,2,4-triazole-3-thiolate, respectively. Similar to the typical reductant I-, the S atoms of thiolate anions interact with the oxidized Z907 (Z907(+)) via the terminal S atoms of the isothiocyanate (NCS) ligands. However, nearly 40% of the atomic charge and spin still remain after complexation. If a second thiolate anion, as well as I-, is considered, the atomic charge and spin are transferred completely. The distances of the formed S-S bonds for the Z907(+)-two anions species correspond to isolated dithiolate radicals. These results suggest that Z907(+) can be completely regenerated by two thiolate anions via a two-step mechanism rather than by only one thiolate anion through a one-step mechanism as previously suggested. Unlike the I-2 molecule, the unfound Z907disulfide complex structure supports the slower recombination process with the disulfide/thiolate electrolyte compared with the I-3(-)/I- system in dye-sensitized solar cells. (C) 2017 Elsevier B.V. All rights reserved.