Economic synthesis of Co 3 S 4 ultrathin nanosheet/reduced graphene oxide composites and their application as an efficient counter electrode for dye-sensitized solar cells

Despite cobalt sulfide nanosheets gain great attention for their excellent electrochemical performance, the lack of economic and scalable synthesis method limits their applications. Herein, a simple and cost-effective noninjection hydrothermal process is proposed to synthesize Co3S4 ultrathin nanosheets on the surface of reduced graphene oxide (rGO) by controlling the polarity of the reaction solution and introducing NH3. Experimental and theory results reveal that the obtained Co3S4 nanosheets have higher electrochemical properties for the reduction of I3− than bulk due to their larger density of electron states in the nearby of Fermi level facilitating fast electron-transfer and providing highly active sites for catalytic reaction. With the synergistic effect of rGO, electrocatalytic performances of Co3S4 nanosheets can be further optimized. The dye-sensitized solar cell (DSSC) device with Co3S4 nanosheet/rGO as counter electrode (CE) material exhibits a power conversion efficiency (PCE) of up to 8.08%, which is superior to that of Co3S4 nanosheet (7.13%) and Pt (7.62%) at the same measurement condition. Moreover, Co3S4 nanosheet/rGO composites show enhanced cycling stability, indicating the great possibility of them for replacing Pt as an advanced CE in DSSCs.