Silane: A new linker for chromophores in dye-sensitised solar cells

A series of ruthenium(II) polypyridyl complexes, with novel silane functionalisation, [Ru(bipy)2(bipy-sil)](PF6)2 (3), [Ru(bipy-sil)2Cl2] (6), and [Ru(bipy-sil)2(NCS)2] (7) have been synthesised and tested as chromophores (dyes) in TiO2 and WO3 based dye-sensitised solar cells (DSSCs). The performance of the respective DSSCs were compared to analogous dyes with ionic carboxylate ([Ru(bipy)2(dcbipy)](PF6)2 (1), [Ru(dcbipy)2Cl2] (4), [Ru(dcbipy)2(NCS)2] (5)) or phosphonate ([Ru(bipy)2(dpipy)](PF6)2 (2)) linking groups. The covalent silane-metal oxide linkage offers much needed improvement to the operating conditions, and lifetime of DSSCs, in terms of pH range and choice of solvent. UV-Vis spectroscopy of the deep-red solutions showed that the bis-bipy-sil complexes absorbed more visible light than the tris-bipy complex, as indicated by the presence of two absorption bands and higher e values. The UV-Vis spectrum of (3) contained a single broad absorption at 400-600 nm with: max = 457 nm; e = 10 520 ± 440 L mol-1 cm-1, whereas two intense broad absorption bands were observed for novel bis-bipy-sil complexes (6): 340-370 nm (max(1) = 365 nm, e(1) = 12 716 ± 180 L mol-1 cm-1); and 440-540 nm (max(2) = 485 nm, e(2) = 11 070 ± 150 L mol-1 cm-1), and (7): 340-400 nm (max = 371 nm, e(1) = 20 690 ± 485 L mol-1 cm-1), and 460-530 nm (max = 500 nm and e(2) = 20 750 ± 487 L mol-1 cm-1). The bands in (7) being significantly more defined.