Functionalized graphene sheets as a versatile replacement for platinum in dye-sensitized solar cells.

Several techniques for fabricating functionalized graphene sheet (FGS) electrodes were tested for catalytic performance in dye-sensitized solar cells (DSSCs). By using ethyl cellulose as a sacrificial binder, and partially thermolyzing it, we were able to create electrodes which exhibited lower effective charge transfer resistance (<1 Ω cm(2)) than the thermally decomposed chloroplatinic acid electrodes traditionally used. This performance was achieved not only for the triiodide/iodide redox couple, but also for the two other major redox mediators used in DSSCs, based on cobalt and sulfur complexes, showing the versatility of the electrode. DSSCs using these FGS electrodes had efficiencies (η) equal to or higher than those using thermally decomposed chloroplatinic acid electrodes in each of the three major redox mediators: I (η(FGS) = 6.8%, η(Pt) = 6.8%), Co (4.5%, 4.4%), S (3.5%, 2.0%). Through an analysis of the thermolysis of the binder and composite material, we determined that the high surface area of an electrode, as determined by nitrogen adsorption, is consistent with but not sufficient for high performing electrodes. Two other important considerations are that (i) enough residue remains in the composite to maintain structural stability and prevent restacking of FGSs upon the introduction of the solvent, and (ii) this residue must not disperse in the electrolyte.