Graphene films decorated with metal sulfide nanoparticles for use as counter electrodes of dye-sensitized solar cells

The composite films of metal sulfide (MS, M = Ni, Co) nanoparticles (NPs)/graphene films were proposed to be novel transparent conductive oxide- and platinum (Pt)-free counter electrodes with high electrocatalytic activity for dye-sensitized solar cells (DSSCs). Such DSSCs show higher photovoltaic conversion efficiencies of 5.25% (NiS/graphene) and 5.04% (CoS/graphene), compared with 5.00% for (Pt/fluorine-doped tin oxide). The excellent DSSC efficiencies are mainly due to the superior electrocatalytic activity of the MS and graphene films, and highly electrical properties of graphene films (9.57 Ω/sq). The excellent charge transfer between MS NPs and graphene films is due to the unique MS NPs and high surface area graphene structure. The graphene films were directly grown on dielectric SiO2 substrates by chemical vapor deposition. MS NPs were uniformly implanted on the graphene films by dip coating of MS precursors M(C3H5OS2)2, and further annealed at 400 °C for 30 min under Ar.