In this paper, it was demonstrated that Na2O can react with CO to produce carbon nanofibers at 500 degrees C and carbon nanosheets at 550 degrees C. Furthermore, the nanosheets exhibited excellent performance as a counter electrode for a dye-sensitized solar cell (DSSC), leading to a high power conversion efficiency of 7.57%. The efficiency is larger than that (4.72%) of a DSSC with the carbon nanofiber counter electrode and even comparable with that of an expensive Pt-based DSSC. Copyright (c) 2015 John Wiley & Sons, Ltd.