Corrole dyes for dye-sensitized solar cells: The crucial role of the dye/semiconductor energy level alignment

A joint experimental and computational study on a series of four β-carboxy-corroles, both in free-base and in copper complexes form, is presented. The main goal of the work is to understand by means of high-level DFT and TDDFT calculations the reasons for the low photovoltaic performances obtained for these dyes when employed in dye-sensitized solar cells. We also report a comparison between the unsubstituted 5-10-15,triphenyl-corrole and his 3-carboxylated analog, in order to investigate the effect of the carboxylic acid on the geometrical, electrochemical and optical properties of these sensitizers. By modeling the adsorption of the investigated dyes on an extended TiO2 nanocluster and by analyzing the Density of State composition of the dye@TiO2 systems, we basically find an unfavorable dye/semiconductor energy level alignment for the electron injection process, possibly accounting for the poor photovoltaic performances of these corroles compounds.