Conversion of Light into Electricity with Trinuclear Ruthenium Complexes Adsorbed on Textured TiO 2 Films

A series of CN‐bridged trinuclear Ru complexes of the general structure [RuL 2 (μ‐(CN)Ru(CN)L 2 ′) 2 ] where L is 2,2′‐bipyridine‐4,4′‐dicarboxylic acid and L′ is 2,2′‐bipyridine ( 1 )2,2′‐bipyridine‐4,4′‐dicarboxylic acid ( 2 ), 4,4′‐dimethyl‐2,2′‐bipyridine ( 3 ), 4,4′‐diphenyl‐2,2′‐bipyridine ( 4 ), 1,10‐phenanthroline ( 5 ), and bathophenanthrolinedisulfonic acid ( 6 ) have been synthesized, and their spectral and electrochemical properties investigated. The two carboxylic functions on the 2,2′‐bipyridine ligand L serve as interlocking groups through which the dye is attached at the surface of TiO 2 films having a specific surface texture. The role of these interlocking groups is to provide strong electronic coupling between the π* orbital of the 2,2′‐bipyridine and the 3d‐wave‐function manifold of the conduction band of the TiO 2 , allowing the charge injection to proceed at quantum yields close to 100 %. The charge injection and recombination dynamics have been studied with colloidal TiO 2 , using laser photolysis technique in conjunction with time‐resolved optical spectroscopy. Photocurrent action spectra obtained from photo‐electrochemical experiments with these trinuclear complexes cover a very broad range in the visible, making them attractive candidates for solar light harvesting. Monochromatic incident photon‐to‐current conversion efficiencies are strikingly high exceeding 80% in some cases. Performance characteristics of regenerative cells operating with these trinuclear complexes and ethanolic triiodide/iodide redox electrolyte have been investigated. Optimal results were obtained with complex 1 which gave a fill factor of 75 % and a power conversion efficiency of 11.3% at 520 nm.