A Titanium Oxo Cluster Model Study of Synergistic Effect of Co-coordinated Dye Ligands on Photocurrent Responses

The use of multiple sensitizers in dye sensitized solar cells has been attractive as a promising way to achieve highly efficient photovoltaic performance. However, except for the complementary absorption, synergistic effects among the dye components have not been well understood. Herein, using ferrocene-1-carboxylate (FcCO₂) and catechol (Cat) as dye ligands, two titanium oxo clusters (TOCs), [Ti₃O(OⁱPr)₆(Cat)(FcCO₂)₂] (1) and [Ti₇O₄(OⁱPr)₈(Cat)₅(FcCO₂)₂] (2), were synthesized and structurally characterized. Another TOC, [Ti₇O₃(OⁱPr)₁₂(Cat)₄( o-BDC)] (3) ( o-BDC = o-benzene dicarboxylate), was also prepared as a contrast. Electronic spectra and theoretical calculations showed that charge transfer occurs from ligands FcCO₂ and Cat to the TiO cluster core and the contribution of redox active FcCO₂ is greater than that of Cat. Using the clusters as TiO-dye pre-anchored precursors, multi-dye sensitized TiO₂ electrodes were prepared. Although the two dyes FcCO₂ and Cat do not complement each other in spectra, a synergistic effect on the enhancement of photocurrent responses was found and discussed in view of the inter-dyes electron communication.