A Significant Improvement in the Electrocatalytic Stability of N-Doped Graphene Nanosheets Used as a Counter Electrode for [Co(bpy)₃]^3+/2+ Based Porphyrin-Sensitized Solar Cells

A significant improvement in efficiency is achieved for porphyrin (YD2-o-C8) based dye-sensitized solar cells, coupled with [Co(bpy)3] 3+/2+ mediator electrolyte. However, the poison of the counter electrode (CE) by the [Co(bpy)3] 3+/2+ mediator remains a significant barrier to producing a reliable high-performance device. In this paper, nitrogen-doped graphene nanosheets (NG) are produced using a low-cost solution-based process and are used as the CE for [Co(bpy)3] 3+/2+ based porphyrin-sensitized solar cells. These produce significantly better electrocatalytic activity than the commonly used Pt CE. The superior performance is a result of the increased number of catalytic sites and the wettable surface that is caused by the substitution of pyridinic and pyrrolic N into the carbon-conjugated lattice. To the authors’ best knowledge, the significantly improved cycling stability (>1000 times) of NG CE for [Co(bpy)3] 3+/2+ redox complexes is demonstrated for the first time.