Aqueous-dispersible graphene (a-dG) sheets were fabricated by reducing the graphite oxide (GO) nanosheets in water in the presence of poly [3-(potassium-6-hexanoate) thiophene-2, 5-diyl] (P3KT) through noncovalent functionalization. The successful reduction of GO was confirmed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The obvious fluorescence quenching of P3KT by a-dG in the solid films due to the efficient charge transfer between P3KT and a-dG demonstrated that a-dG could be expected to be used as the electron acceptor in the polymer solar cell (PSC) devices. "Green" PSCs with the structure of ITO/PEDOT: PSS/P3KT: a-dG/ZnO/Al, where P3KT acts as donor, aqueous-dispersible noncovalent functionalized graphene sheets as acceptor and ZnO as both electron transporting and hole blocking layer, have been fabricated using water as the solvent for the active layer. The short-circuit current (J(sc)), open circuit voltage (V-oc) and power conversion efficiency (PCE) of the devices with P3KT: a-dG composite film as the active layer increased compared with those of the devices with P3KT pure film as the active layer, which indicated that a-dG can be used as the electron acceptor in PSCs. (C) 2011 Elsevier B.V. All rights reserved.