Polypyridyl ruthenium complexes containing anchoring nitrile groups as TiO2 sensitizers for application in solar cells

Abstract

Ruthenium polypyridyl complexes of general formula [Ru(bpy)3-x(Mebpy-CN)x]2+ ( x = 1,2 and 3, bpy = 2,2´-bipyridine, Mebpy-CN = 4-methyl-2,2´-bipyridine-4´-carbonitrile) can be used as visible dyes in novel solar cells formed with a porous TiO2 film (1 cm2), Pt counter-electrode and iodine/iodide as the redox mediator electrolyte dissolved in a polymeric matrix. These complexes can be anchored over the surface of nanocrystalline TiO2 through nitrile groups, as evidenced by Raman spectra of the adsorbed species. Irradiated by a solar simulator (67 mW cm-2), the cells assembled with the Ru complexes with x = 2 and 3 as TiO2 sensitizers exhibit almost identical current-potential curves, with short-circuit photocurrents of 1.25 mA cm-2, fill factors of 0.5 and overall efficiencies around 0.44 %. The Ru complex with x = 1 and the Re complex did not perform as well as sensitizers. These data were consistent with results obtained from quantum efficiency curves and impedance spectra. We conclude that complexes with nitrile groups as anchoring entities are promising candidates for designing efficient DSCCs