Conversion of Light into Electricity with Trinuclear Ruthenium Complexes Adsorbed on Textured TiO2 Films

Abstract

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.