N-Doped Graphene Nanoplatelets as Superior Metal-Free Counter Electrodes for Organic Dye-Sensitized Solar Cells

Highly efficient counter electrodes (CEs) for dye-sensitized solar cells (DSScs) were developed using thin films of scalable and high-quality, nitrogen-doped graphene nanoplatelets (NGnP), which was synthesized by a simple two-step reaction sequence. The resultant NGnP was deposited on fluorine-doped SnO2 (FTO)/glass substrates by using electrospray (e-spray) coating, and their electrocatalytic activities were systematically evaluated for Co(bpy)(3)(3+/2+) redox couple in DSSCs with an organic sensitizer. The e-sprayed NGnP thin films exhibited outstanding performances as CEs for DSSCs. The optimized NGnP electrode showed better electrochemical stability under prolonged cycling potential, and its R-ct at the interface of the CE/electrolyte decreased down to 1.73 Omega cm(2), a value much lower than that of the Pt electrode (3.15 Omega cm(2)). The DSSC with the optimized NGnP-CE had a higher fill factor (FF, 74.2%) and a cell efficiency (9.05%), whereas those of the DSSC using Pt-CE were only 70.6% and 8.43%, respectively. To the best of our knowledge, the extraordinarily better current voltage characteristics of the DSSC-NGnP outperforming the DSSC-Pt for the Co(bpy)(3)(3+/2+) redox couple (in paticular, FF and short circuit current, J(sc)) is highlighted for the first time.