In situ growth of Co9S8 nanocrystals on reduced graphene oxide for the enhanced catalytic performance of dye-sensitized solar cell

Abstract The counter electrode material of dye-sensitized solar cells (DSSCs) with excellent catalytic activity and fast electron transfer ability could effectively improve the overall photoelectrical conversion efficiency (PCE). In this work, monodispersed Co 9 S 8 nanocrystals (NCs) were in situ grown on the surface of the reduced graphene oxide (RGO) through a simple hot-injection method. Due to the confinement of organic ligand oleylamine, the Co 9 S 8 NCs with the size of ca. 8 nm were mainly dispersed on the surface of RGO (Co 9 S 8 /RGO). The Co 9 S 8 /RGO composite with the optimal contents (RGO contents of 44.4 wt%) was prepared by controlling the amount of graphene oxide (GO) added, which possessed the optimal catalytic active site numbers and electron transfer ability as it showed a higher PCE of 7.31%. It was higher than that of the solo Co 9 S 8 NCs and comparable to that of the Pt (7.72%). The electrochemical characteristics (cyclic voltammetry, Tafel polarization curve, and electrochemical impedance spectroscopy) confirmed their excellent electrocatalytic activity towards I 3 − /I − redox reduction. Furthermore, the calculations based on the density functional theory (DFT) revealed that the absorption energy of I 3 − on the Co site at the interface of Co 9 S 8 /RGO composite was −1.881 eV, which was higher than that of solo Co 9 S 8 NCs (−1.078 eV). So, Co atoms in the Co 9 S 8 /RGO interface was the predominant catalytic active center for the I 3 − reduction. This in situ growth strategy provided a new strategy for the preparation of electrocatalytic materials.