Preparation and application of new ruthenium(II) polypyridyl complexes as sensitizers for nanocrystalline TiO2

A series of Ru-(II) polypyridyl complexes, containing carboxylicand sulphonic ‘anchor’ groups, were synthesized as sensitizers for nanocrystalline TiO2. Depending on number and type of ligands the sensitizers are divided into three classes: tris-homoleptic complexes 1a–d, tris-heteroleptic complexes 2a–d and bis-complexes 3a–f. The compounds were characterized and the photophysical and electrochemical properties were examined. These studies proved the suitability of 1a–3f as sensitizers for TiO2-based photoelectrochemical ‘Graetzel’-type solar cells. A comparison of the performance of the complexes 1a–3f in the cell relative to Ru(dcbpy)2(NCS)2 3d as internal standard for mean efficiency η is presented, whereby Ru(dcphen)2(NCS)2 3f is shown to have an efficiency of ηrel.=62.3% relative to 3d. A possible reason for the particular efficiency of 3d as sensitizer is discussed. ©2000 Elsevier Science S.A. All rights reserved.