XPS studies of Ru-polypyridine complexes for solar cell applications

Abstract

A series of Ru-polypyridine dyes has been studied with electron spectroscopy using AlKα and synchrotron radiation. Both pure complexes and complexes adsorbed on nanostructured TiO2 (anatase) surfaces have been examined and special emphasis was given to the dye complex cis-bis(4,4′-dicarboxy-2,2′-bipyridine)-bis-(isothiocyanato)-ruthenium(II) [Ru(dcbpy)2(NCS)2]. The measurements provide information concerning the energy level matching between the dyes and the TiO2, which is of importance in photoinduced charge transfer reactions and in applications such as dye-sensitized solar cells. The measurements also support the general picture of bonding of carboxylated complexes to the surfaces via the carboxyl groups of a single bi-isonicotinic acid ligand, and that, for Ru(dcbpy)2(NCS)2, the NCS-ligand–TiO2 interaction is small. Corroborative support is provided via quantum chemical calculations on the ligand (bi-isonicotinic acid) adsorbed on a TiO2 anatase (101) surface.