Supramolecular interactions of chenodeoxycholic acid increase the efficiency of dye-sensitized solar cells based on a cobalt electrolyte

A combined experimental and computational study is carried out to understand the nature of the interfaces between dye-sensitized TiO2 and cobalt-based electrolyte in the presence of a prototype coabsorbent, chenodeoxycholic acid (CDCA), employed in dye-sensitized solar cells (DSCs). It was recently reported that including CDCA both in the dye and in the electrolyte solutions substantially improved the performance of DSCs based on a Fc/Fc(+) electrolyte (Daeneke et al. Nat. Chem. 2011, 30755). Here, we evaluate the individual and combined effect of CDCA as a surface coadsorbent and as an additive in DSCs based on a Co(II)/Co(III) electrolyte, in combination with two prototypical Ru(II) dyes, N719 and Z907. For both dyes, the concomitant use of CDCA in the dye bath and in the electrolyte solution leads to a significant improvement, by about, a factor of 2, of the DSCs photovoltaic performances, allowing us to reach 5.3% efficiency with Z907. FT-IR analyses conducted on the solid and TiO2-adsorbed CDCA highlight the presence of surface-adsorbed interacting CDCA molecules, possibly creating a bulky insulating network on the TiO2 surface. Computational analyses have been carried out to gain insight into the nature of the supramolecular aggregates occurring for CDCA on the TiO2 surface.