Nitrogen plasma modified CVD grown graphene as counter electrodes for bifacial dye-sensitized solar cells

In this study, we report modification of few-layer graphene grown by chemical vapour deposition via nitrogen plasma ion irradiation and its application as counter electrodes in bifacial dye-sensitized solar cells (DSSCs). The incorporation of nitrogen (N) atoms and defects are confirmed by X-ray photoelectron spectroscopy and Raman spectroscopy. Electrochemical impedance spectroscopy measurement reveals that the charge transfer resistance of graphene for triiodide reduction shows a decrease with increasing plasma treatment time, which is attributed to the increase of catalytic sites. The energy conversion efficiency of 3.12% is obtained when using the N-doped graphene films as counter electrodes, which is nearly 3 times higher than that of the pristine graphene films in DSSCs. More importantly, the DSSCs based on N-doped graphene CEs show much higher ηrear/ηfront ratio and better long-term stability than that based on Pt CEs. These results reveal the promising potential of this transparent N-doped graphene CEs in low cost and effective bifacial DSSCs.