Moderately reduced graphene oxide (GO) films were fabricated by simple and fast thermal treatment of solution processed GO, and their application as an alternative to conventional Pt counter electrode in dye-sensitized solar cells (DSSCs) was investigated. GO without thermal treatment and thermally treated GO at 150 degrees C showed low efficiency of similar to 0.5%, whereas cell performance was significantly improved by applying thermal treatment over 250 degrees C. In particular, the DSSC with GO thermally treated at 350 degrees C exhibited the highest performance with open-circuit voltage (V-oc) of 0.66 V. short-circuit current density (J(sc)) of 16.35 mA/cm(2), F.F. of 33.33%, and overall power conversion efficiency (PCE) of 3.60%. Moderate reduction of GO by simple thermal treatment over 250 degrees C was confirmed through the measurements of X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). Enhancement of efficiency after high temperature thermal treatment might be attributed to the improved electrical conductivities and higher catalytic activities, resulting from the reduction of GO. (c) 2012 Elsevier Ltd. All rights reserved.