Abstract: Copper sulfide (Cu_xS)/reduced graphene oxide (RGO) nanocomposites were prepared by a one-pot hydrothermal method with various contents of GO in the initial precursor. The nanocomposites were first blended with a polyvinylidene fluoride binder, then coated onto SnO_x^2-F_x substrates,which were used as the counter electrodes (CEs) of quantum dot solar cells (QDSCs) using a CdS-sensitized TiO₂ as a photoanode. The microstructure and performance of the CEs were characterized by FE-SEM, XRD, Raman spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Results show that the Cu_xS/RGO CEs are superior to the conventional Cu₂S/brass CE. The stoichiometry and morphology of the Cu_xS nanocrystals are significantly influenced by the initial GO content in the precursor. A Cu_xS/RGO nanocomposite with more active sites for effective S_x^2- ion reduction in a polysulfide electrolyte (S^2-/S_x^2-) is optimally obtained at a medium GO content in the precursor. The QDSC assembled with the optimized Cu_xS/RGO CE exhibits a reproducible high and stable power conversion efficiency of 2.36% under an illumination intensity of 100 mW/cm², which is higher than the value (1.57%) of the cell with the Cu₂S/brass CE. The improved performance is attributed to the synergistic effect between the Cu_xS nanocrystals and conductive RGO in the Cu_xS/RGO CE, where RGO acts as both a co-catalyst to accelerate the polysulfide reduction and a conductivity promoter to decrease the series resistance of the CE.