High-performance dye-sensitized solar cells using edge-halogenated graphene nanoplatelets as counter electrodes

Abstract Edge-selectively halogenated graphene nanoplatelets (XGnPs, X=Cl, Br, and I) were prepared by the mechanochemically driven reaction between graphite and diatomic halogen molecules (Cl 2 , Br 2 or I 2 ). The contents of halogens (Cl, Br, and I) in XGnPs were 3.18, 1.77, and 0.66 at%, respectively, by X-ray photoelectron spectroscopy. The XGnPs as counter electrodes (CEs) showed remarkably enhanced electrocatalytic activities toward Co ( bpy ) 3 3 + reduction reaction in dye-sensitized solar cells (DSSCs) with an excellent electrochemical stability. Amongst XGnPs, IGnP-CE demonstrated the lowest charge-transfer resistance ( R ct ) of 0.46 Ω cm 2 at the CE/electrolyte interface. This value is much lower than that of Pt-CE (0.81 Ω cm 2 ). In addition, the DSSC with IGnP-CE had the highest fill factor (71.3%) and cell efficiency (10.31%), whereas those of DSSCs with Pt-CE were only 70.6% and 9.92%, respectively.