Ruthenium oxyquinolate complexes for dye-sensitized solar cells

The ever-increasing demand for energy of our technological and “fossil fuel-depending” society prompts humanity to point towards alternative renewable sources; in this context the Sun is a very attractive green energy source due to its ubiquitous availability and its huge radiant power. Since the first publication in 1993 by Graetzel and coworkers of the so-called dye-sensitized solar cell (DSSC), research groups all over the world have engaged in the improvement of the low power conversion efficiencies of such photovoltaic devices. Surely such improvements could be obtained studying the behavior of the dyes implemented in the cells as sensitizers for a high energy-gap semiconductor (e.g. TiO2), in order to synthesize new much more performing molecules. Recently our research team has been involved in such field, discovering different families of transition-metal complexes of particular interest as materials for sun-light harvesting. This presentation will be focused on the synthesis and successive multi-technique characterization of Ru(II) complexes bearing a chelating hydroxyquinolate ligand (see figure) as a new functionalizable moiety for the development of novel dyes for DSSCs. The work regards the set up of a new and convenient synthesis of the two complexes mediated by microwave irradiation (which leads to a drastic reduction of the reaction time, from 18 hours to 10 minutes) and their electrochemical characterization. Particular attention will be devoted to a mechanistic-type study obtained by comparison of cyclo- and differential pulse voltammetric patterns of both free-ligands and related complexes; key energetic parameters (e.g. HOMO and LUMO energy, E1/2 dye+|dye), useful to evaluate performance of the complexes as sensitizers in DSSCs, will be presented. Photovoltaic characterization of the devices will also be shown.