We report a combined experimental and computational investigation to understand the nature of the interactions between cobalt redox mediators and TiO(2) surfaces sensitized by ruthenium and organic dyes, and their impact on the performance of the corresponding dye-sensitized solar cells (DSSCs). We focus on different ruthenium dyes and fully organic dyes, to understand the dramatic loss of efficiency observed for the prototype Ru(II) N719 dye in conjunction with cobalt electrolytes. Both N719- and Z907-based DSSCs showed an increased lifetime in iodine-based electrolyte compared to the cobalt-based redox shuttle, while the organic D21L6 and D25L6 dyes, endowed with long alkoxy chains, show no significant change in the electron lifetime regardless of employed electrolyte and deliver a high photovoltaic efficiency of 6.5% with a cobalt electrolyte. Ab initio molecular dynamics simulations show the formation of a complex between the cobalt electrolyte and the surface-adsorbed ruthenium dye, which brings the [Co(bpy)(3)](3+) species into contact with the TiO(2) surface. This translates into a high probability of intercepting TiO(2)-injected electrons by the oxidized [Co(bpy)(3)](3+) species, lying close to the N719-sensitized TiO(2) surface. Investigation of the dye regeneration mechanism by the cobalt electrolyte in the Marcus theory framework led to substantially different reorganization energies for the high-spin (HS) and low-spin (LS) reaction pathways. Our calculated reorganization energies for the LS pathways are in excellent agreement with recent data for a series of cobalt complexes, lending support to the proposed regeneration pathway. Finally, we systematically investigate a series of Co(II)/Co(III) complexes to gauge the impact of ligand substitution and of metal coordination (tris-bidentate vs bis-tridentate) on the HS/LS energy difference and reorganization energies. Our results allow us to trace structure/property relations required for further development of cobalt electrolytes for DSSCs.

A combined experimental and computational study is carried out to understand the nature of the interfaces between dye-sensitized TiO 2 and cobalt-based electrolyte in the presence of a prototype co-absorbent, 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, 3,1755). Here we evaluate the individual and combined effect of CDCA as a surface co-adsorbent 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 ca. a factor 2, of the DSCs photovoltaic performances, allowing us to reach 5.3% efficiency with Z907. FT-IR analyses conducted on the solid and TiO 2-adsorbed CDCA highlight the presence of surface-adsorbed interacting CDCA molecules, possibly creating a bulky insulating network on the TiO 2 surface. Computational analyses have been carried out to gain insight into the nature of the supramolecular aggregates occurring for CDCA on the TiO 2 surface.

We describe some copper(II) complexes with tridentate anionic Schiff bases, L -, derived from the monocondensation of some 5-substituted salicylaldehydes (5-G-salH, G = H, NO 2 and OMe) with ethylenediamine (en) or 1,3-diaminopropane (tn 2+ compounds have been obtained, and factors affecting the nuclearity of complexes were investigated and found to depend on reaction conditions, the nature