Investigation of a new bis(carboxylate)triazole-based anchoring ligand for dye solar cell chromophore complexes

Abstract

A novel anchoring ligand for dye-sensitised solar cell chromophoric complexes, 1-(2,2′-bipyrid-4-yl)-1,2,3-triazole-4,5-dicarboxylic acid (dctzbpy), is described. The new dye complexes [Ru(bpy)₂(dctzbpy)][PF₆]₂ (AS16), [Ir(ppy)₂(dctzbpy)][PF₆] (AS17) and [Re(dctzbpy)(CO)₃Cl] (AS18) were prepared in a two stage procedure with intermediate isolation of their diester analogues, AS16-Et₂, AS17-Et₂ and AS18-Et₂ respectively. Electrochemical analysis of AS16-Et₂, AS17-Et₂ and AS18-Et₂ reveal reduction potentials in the range −1.50 to −1.59 V (vs. Fc⁺/Fc) which are cathodically shifted with respect to that of the model complex [Ru(bpy)₂(dcbH₂)]²⁺ (1) (E_red = −1.34 V, dcbH₂ = 2,2′-bipyridyl-4,4′-dicarboxylic acid). This therefore demonstrates that the LUMO of the complex is correctly positioned for favourable electron transfer into the TiO₂ conduction band upon photoexcitation. The higher energy LUMOs for AS16 to AS18 and a larger HOMO–LUMO gap result in blue-shifted absorption spectra and hence reduced light harvesting efficiency relative to their dcbH₂ analogues. Preliminary tests on TiO₂ n-type and NiO p-type DSSCs have been carried out. In the cases of the Ir(III) and Re(I) based dyes AS17 and AS18 these show inferior performance to their dcbH₂ analogues. However, the Ru(II) dye AS16 (η = 0.61%) exhibits significantly greater efficiency than 1 (η = 0.1%). In a p-type cell AS16 shows the highest photovoltaic efficiency (η = 0.028%), almost three times that of cells incorporating the benchmark dye coumarin C343.