Graphene-mediated highly-dispersed MoS2 nanosheets with enhanced triiodide reduction activity for dye-sensitized solar cells

Novel composites made of two dimensional (2D) MoS2 nanosheets and graphene (G) have been fabricated by a combined approach of chemical vapor deposition and hydrothermal technique. The G film helps to mediate the growth and dispersion of MoS2 nanosheets, of which the unique role of G in the MoS2 growth is revealed by density functional theory study. The results show that the hexagonal lattice carbon of the G film can easily interact with sulfur species derived from reaction precursors, which favors the uniform growth of 2D MoS2. The unique function of the G film demonstrated here can be extended to other carbon substrates for growing 2D MoS2 nanosheets. The G-MoS2 composites consisting of two types of 2D materials are tested as the binder-free counter electrodes (CEs) for dye-sensitized solar cells, showing a high power conversion efficiency of 7.1% that is comparable to the expensive Pt CEs. The 2D G film in the hybrids has two functions: the active sites for dispersing the electrochemically active MoS2 crystals and the high electrical conducting matrix for fast charge transfer. This synergistic effect may help to shed a light on the functionalization of other inorganic materials to G for advanced energy applications.