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

Abstract 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 Co 3 S 4 ultrathin nanosheets on the surface of reduced graphene oxide (rGO) by controlling the polarity of the reaction solution and introducing NH 3 . Experimental and theory results reveal that the obtained Co 3 S 4 nanosheets have higher electrochemical properties for the reduction of I 3 − 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 Co 3 S 4 nanosheets can be further optimized. The dye-sensitized solar cell (DSSC) device with Co 3 S 4 nanosheet/rGO as counter electrode (CE) material exhibits a power conversion efficiency (PCE) of up to 8.08%, which is superior to that of Co 3 S 4 nanosheet (7.13%) and Pt (7.62%) at the same measurement condition. Moreover, Co 3 S 4 nanosheet/rGO composites show enhanced cycling stability, indicating the great possibility of them for replacing Pt as an advanced CE in DSSCs.