Enhanced Charge-Transfer Performance of Photoelectrode Based on Interface Modification in Dye-Sensitized Solar Cells

A simple FTO conductive glass substrate decoration by graphene nanosheets before the manufacture of TiO2 photoelectrode via a layer by layer assembly process was proposed in dye-sensitized solar cells (DSSCs). FESEM images indicated that graphene nanosheets overlaid on FTO glass clearly. The J-V measurements of DSSCs demonstrated that introduction of graphene nanosheets on photoelectrode certainly presented obvious influence on photovoltaic performance. Exactly, as the amount of graphene additions increasing, conversion efficiencies of DSSCs firstly improved from 5.01% to 5.36% and then reduced to 3.67%, compared to the efficiency of 4.72% with bare FTO glass. EIS results exhibited that the charge transfer resistance (R-3) at TiO2-FTO glass interface decreased as the addition of graphene nanosheets. When the substrate was treated by graphene solution twice, R3 of corresponded DSSC (G2) was only 9.31 Omega, which is remarkably lower than that of the untreated one (15.01 Omega). This result revealed the interface modification function of graphene between FTO and TiO2 film. However, as the treatment times increased further, R-3 rose to 11.32 Omega. This trend could be attributed to the electrocatalytic activity of graphene for I-3(-) reduction which would be enhanced as the thickness of graphene film increased. This paper expounded that graphene nanosheets surface treatment of photoelectrode was an effective way to improve their photovoltaic performance in DSSCs.