This study reports on the synthesis of a PtCo alloy/reduce graphene oxide (RGO) nanohybrid materials and their application as an efficient counter electrodes (CEs) in dye–sensitized solar cells (DSCs). Bimetallic Pt_0.1Co_0.9 nanoparticles (NPs) with average size of ~ 5 nm were successfully and uniformly immobilized on the surface of RGO after co-reduction of metal precursor ions and graphene oxide into bimetallic alloy and RGO, respectively, via dry plasma reduction (DPR) under an atmospheric pressure and near room temperature. Furthermore, the set of bimetallic PtCo/RGO nanohybrids were also synthesized using various volume ratios of Pt to Co precursors. Uniform and dense distribution of bimetallic PtCo NPs on the RGO surface was obtained. The highest electrocatalytic performance, which corresponded to the lowest charge transfer resistance of 2.26 Ω, was achieved with the Pt_0.1Co_0.9 NPs/RGO nanohybrid. The application of developed nanohybrid as an alternative CE for DSCs leads to increase in efficiency by 5.7% over that of the Pt/RGO-based DSC, and by 40.6% over the efficiency of the Pt-free device. We believe that this work provides an effective strategy for optimizing Pt utilization in photovoltaic-device targeted nanohybrid, suggesting the decrease of the production cost of DSCs along with the improvement of efficiency.