Effect of the Ligand Structure on the Efficiency of Electron Injection from Excited Ru−Phenanthroline Complexes to Nanocrystalline TiO2 Films

Abstract

We previously reported that the number of anchoring carboxyl groups affects the solar cell performance of dye-sensitized nanocrystalline TiO2 solar cells using Ru−phenanthroline complexes as the sensitizer. To understand the mechanism in detail, the electron injection efficiency of sensitizing dyes adsorbed on nanocrystalline TiO2 films has been studied by transient absorption spectroscopy. We found that the efficiency of electron injection is strongly affected by the number of carboxyl groups of the sensitizing dye, i.e., the efficiency of cis-bis(4,7-dicarboxy-1,10-phenanthroline)dithiocyanato ruthenium(II) (with four carboxyl groups) adsorbed on nanocrystalline TiO2 films (DCP2/TiO2) being 4 times as large as that of cis-(4-monocarboxy-1,10-phenanthroline)(1,10-phenanthroline)dithiocyanato ruthenium(II) (with one carboxyl group) adsorbed on the same films (MCPP/TiO2). From the analysis of the time profile of the transient absorption, we conclude that the low efficiency of MCPP/TiO2 is due to the presen...