Graphene nanoplatelet cathode for Co(III)/(II) mediated dye-sensitized solar cells.

Graphene nanoplatelets (GNP) in the form of thin semitransparent film on F-doped SnO(2) (FTO) exhibit high electrocatalytic activity for Co(L)(2); where L is 6-(1H-pyrazol-1-yl)-2,2'-bipyridine. The exchange current densities for the Co(2+/3+)(L)(2) redox reaction scaled linearly with the GNP film's optical absorbance, and they were by 1-2 orders of magnitude larger than those for the I(3)(-)/I(-) couple on the same electrode. The electrocatalytic activity of GNP films with optical transmission below 88% is outperforming the activity of platinized FTO for the Co(2+/3+)(L)(2) redox reaction. Dye-sensitized solar cells with Y123 dye adsorbed on TiO(2) photoanode achieved energy conversion efficiencies between 8 and 10% for both GNP and Pt-based cathodes. However, the cell with GNP cathode is superior to that with Pt-FTO cathode particularly in fill factors and in the efficiency at higher illumination intensities.