Highly crystalline graphene/carbon black composite counter electrodes, possessing advantages of both rapid electron transport of graphene and high surface area of carbon black, have been prepared using a facile approach. Tuning composite content allows for the fabrication of high-efficiency dye-sensitized solar cells (DSSCs) in this work. The ratio of graphene and carbon black at ca. 1:3 in weight has been confirmed optimum for synthesizing the composite counter electrode. By comparison with those made of either highly crystalline graphene or carbon black, the DSSC based on composite counter electrode has higher conversion efficiency. Moreover, not only does our DSSCs have comparable performance to that of the Pt-based DSSC, but is more cost-effective. Additionally, the chemical catalysis and stability of composite counter electrodes toward I reduction, and the interfacial charge transfer have been quantitatively investigated by cyclic voltammetry and electrochemical impedance spectra. The results have revealed that the content of graphene and carbon black in composite counter electrodes is very important for fabricating the DSSCs with high catalytic performance and fast interfacial electron transfer. (C) 2013 Elsevier Ltd. All rights reserved.