Bifurcation of Regeneration and Recombination in Dye-Sensitized Solar Cells via Electronic Manipulation of Tandem Cobalt Redox Shuttles.

A cobalt(IV/III) redox shuttle, cobalt tris(2-(p-tolyl)pyridine), [Co(ptpy)3]+/0, was synthesized and investigated for use in dye-sensitized solar cells, DSSCs. An incredibly fast self-exchange rate constant of (9.2 ± 3.9) × 108 M-1 s-1 was determined for [Co(ptpy)3]+/0, making it an ideal candidate for dye regeneration. To avoid fast recombination and solubility limitations, we utilized a tandem electrolyte containing [Co(ptpy)3]+/0 and cobalt tris(2,2'-bipyridine), [Co(bpy)3]3+/2+. An improved short circuit current density is achieved for DSSCs employing the tandem electrolyte, compared to electrolytes containing only [Co(bpy)3]3+/2+, consistent with superior dye regeneration expected based on predictions using Marcus theory, which is also discussed.