A composite film of molybdenum diselenide nanosheets and poly(3,4-ethylenedioxythiophene):poly (styrenesulfonate) (MoSe2 NS/PEDOT:PSS) was prepared for the counter electrode (CE) of a dye-sensitized solar cell (DSSC), via a low-cost drop-coating method. The two-dimensional (2D) nanosheets of MoSe2 (MoSe2 NS) were aimed to provide the composite film not only a large amount of electrocatalytic active sites but also orientational pathways for electron transfer, from the conducting substrate of the CE to the interface at the CE electrolyte. The PEDOT:PSS acts as the conductive matrix for the composite film, and also enables multiple interfacial electron transfer pathways between the MoSe2 NS and the substrate. Owing to the combination of the advantages of both MoSe2 NS and PEDOT:PSS, the DSSC with the composite film of MoSe2 NS/PEDOT:PSS on its CE exhibited a power conversion efficiency (eta) of 7.58 +/- 0.05%, which is comparable to that of the cell with a Pt CE (7.81 +/- 0.03%). The counter electrode films were characterized by scanning electron microscopy. Various electrochemical analyses, including those with cyclic voltammetry, rotating disk electrode, Tafel polarization curves, and electrochemical impedance spectroscopy, were performed intending to quantify the electrocatalytic ability of the counter electrode films; these techniques were able to precisely distinguish the functions of MoSe2 NS and PEDOT:PSS in the composite films; the former worked as an electrocatalyst and the latter as a conductive binder. Incident photon-to-current conversion efficiency (IPCE) was used to substantiate the photovoltaic parameters. When the MoSe2 NS/PEDOT:PSS composite film was coated on a flexible titanium (Ti) foil, the pertinent DSSC showed even a higher eta of 8.51 +/- 0.05%, as compared to a lower eta of 8.21 +/- 0.02% using the Pt-coated Ti foil CE. The results indicate the promising potential of MoSe2 NS/PEDOT:PSS composite film to replace the expensive Pt. (C) 2016 Elsevier Ltd. All rights reserved.