Ru(ii) sensitizers with a tridentate heterocyclic cyclometalate for dye-sensitized solar cells

A new series of bis-tridentate, thiocyanate-free Ru(ii) complexes (TF-21-TF-24), containing the 2-azolyl-6-phenylpyridine cyclometalate, were synthesized. Upon switching from a pyrazolyl to a more electron deficient triazolyl moiety, the oxidation potentials were fine-tuned to readily accept electrons from the I^-/I₃^- redox couple, so that the dye regeneration proceeds efficiently amid the device operation. This, together with high concentrations of 1,3-dimethylimidazolium iodide in the electrolyte which accelerates dye regeneration, attains a short-circuit photocurrent density as high as 18.09 mA cm^-2 and an overall efficiency of 9.04%. The trifling decrease (3-6%) in efficiency after 1000 h of illumination at 60°C manifests the high device stability, due to the much suppressed solvent volatility in combination with the robust bis-tridentate structure involved in cyclometalating the 2-azolyl-6-phenylpyridine ancillary.