Functional Supramolecular Ruthenium Cyclodextrin Dyes for Nanocrystalline Solar Cells

A supramolecular complex [Ru(dcb)2(α‐CD‐5‐bpy)]Cl2 (1‐α‐CD) (dcb = 4,4′‐dicarboxyl‐2,2′‐bipyridine, α‐CD‐5‐bpy = 6‐mono[5‐methyl(5′‐methyl‐2,2′‐bipyridyl)]‐permethylated α‐CD) (CD: cyclodextrin) based on a ruthenium tris‐bipyridyl core with an appended α‐CD cavity is designed and synthesised, in order to facilitate dye/redox couple interaction and dye regeneration in nanocrystalline TiO2 solar cells. The luminescent complex is fully characterized and anchored on mesoporous titania electrodes showing increased power‐conversion efficiency in solid‐state dye‐sensitized solar cells using a composite polymer electrolyte. Direct comparison of the properties of the CD complex with an analogous ruthenium complex [Ru(dcb)2(5,5′‐dmbpy)]Cl2 (2) (5,5′‐dmbpy = 5,5′‐dimethylbipyridine) without the CD cavity reveals that the photovoltaic performance of 1‐α‐CD is enhanced by about 40 % compared to 2. Independent studies have shown complexation of the iodide redox couple to the CD in 1‐α‐CD. These results indicate that the CD moiety is able to act as a mediator and fine tune the photoelectrode/electrolyte interface.