Highly efficient metal-free sulfur-doped and nitrogen and sulfur dual-doped reduced graphene oxide counter electrodes for dye-sensitized solar cells

Developing metal-free electrocatalysts with both high performance and low cost for the reduction reaction at the cathode of dye-sensitized solar cells (DSCs) is critical for further cost reduction and large-scale implementation of DSCs. Here, sulfur-doped reduced graphene oxide (SRGO) and nitrogen and sulfur dual-doped reduced graphene oxide (NSRGO) were applied as highly efficient metal-free electrocatalysts for DSCs in disulfide/thiolate redox electrolytes. It was found that SRGO and NSRGO exhibited outstanding electrochemical performance toward catalyzing the disulfide/thiolate redox couple. The DSC devices based on SRGO and NSRGO counter electrodes showed power conversion efficiency of 4.23% and 4.73%, respectively. In addition, the obtained SRGO and NSRGO also presented catalytic activity higher than that of the platinum electrodes for Co(bpy)₃^3+/2+ redox mediators. The currently reported SRGO and NSRGO demonstrate not only the attractive feasibility of replacing platinum cathodes with abundant carbon materials for novel iodine-free electrolytes but also that the judicious heteroatom doping of graphene oxide might open promising directions for further cathode candidates for iodine-free DSCs.