Dye-sensitized solar cells: Driving-force effects on electron recombination dynamics with cobalt-based shuttles

A series of cobalt-containing redox couples, based on [Co(1, 10-phenanthroline)₃](ClO₄)₂ and its derivatives, were prepared for use as regenerators/shuttles in dye-sensitized solar cells featuring modified TiO₂ photoelectrodes. Surface modification and trap-state passivation of the TiO₂ nanoparticle film electrodes were accomplished via atomic layer deposition of an ultrathin alumina coating. Electron lifetimes were then extracted from open-circuit voltage decay measurements. Cells employing alumina barrier/passivation layers exhibited higher open-circuit voltages as shuttles with more positive redox potentials were used, with the Co(5-nitro-phen)₃^3+/2+ couple exhibiting the highest V_∞ (0.844 V). Analysis of the open-circuit voltages and electron lifetimes indicate Marcus normal-region behavior for back electron transfer from the TiO₂ photoanode to these compounds.