Nitrogen-doped graphene (NDG) sheets are prepared by a hydrothermal reduction of graphite oxide using ammonia as the nitrogen source and employed as the catalyst for triiodide reduction to fabricate counter electrodes in dye-sensitized solar cells. It is found that chemical reduction and nitrogen doping of graphite oxide are achieved simultaneously via a simple hydrothermal process. Electrochemical impedance spectroscopy analysis reveals that the charge-transfer resistance of NDG electrode decreases with increasing the NDG loading. The electrode with a NDG loading of 20 mu g cm(2) shows a charge-transfer resistance of 0.9 Omega cm(2), which is much lower than that of pristine graphene electrode. Such electrocatalytic activity enhancement is mainly attributed to the structural defects and edge plane exposure in NDG. This enhanced electrochemical property is beneficial for improving the photovoltaic performance of dyesensitized solar cells. Under 1 sun illumination (AM 1.5), the dye-sensitized solar cell with NDG electrode shows an energy conversion efficiency of 7.01%, which is comparable to that of the cell with Pt electrode. (C) 2013 Elsevier Ltd. All rights reserved.