Dually functional, N-doped porous graphene foams as counter electrodes for dye-sensitized solar cells

A series of nitrogen-doped porous graphene foams (NPGFs) have been prepared by hydrothermally treating a mixed solution of graphite oxide (GO) and ammonia. The NPGFs are used as the counter electrode (CE) material for dye-sensitized solar cells (DSCs) in conjunction with the conventional iodide-based electrolyte and the recently developed sulfide-based electrolyte. Tafel-polarization tests and electrochemical impedance spectroscopic (EIS) measurements confirmed that the NPGFs work efficiently in both electrolyte systems, and under air mass (AM) 1.5G 100 mW cm^-2 light illumination, optimal efficiencies of 4.5% and 2.1% were obtained for the iodide-based electrolyte and sulfide-based electrolyte, respectively. To the best of our knowledge, this is the first study on N-doped graphene CEs in conjunction with sulfide-based electrolytes and therefore, the current results are deemed to provide new insights into developing novel low-cost and metal-free CEs for DSCs.