Incorporation of Graphenes in Nanostructured TiO2 Films via Molecular Grafting for Dye-Sensitized Solar Cell Application

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Abstract
This paper presents a systematic investigation on the incorporation of chemical exfoliation graphene sheets (GS) in TiO2 nanoparticle films via a molecular grafting method for dye-sensitized solar cells (DSSCs). By controlling the oxidation time in the chemical exfoliation process, both high conductivity of reduced GS and good attachment of TiO2 nanoparticles on the GS were achieved. Uniform GS/TiO2 composite films with large areas on conductive glass were prepared by electrophoretic deposition, and the incorporation of GS significantly improved the conductivity of the TiO2 nanoparticle film by more than 2 orders of magnitude. Moreover, the power conversion efficiency for DSSC based on GS/TiO2 composite films is more than 5 times higher than that based on TiO2 alone, indicating that the incorporation of GS is an efficient means for enhancing the photovoltaic (PV) performance. The better PV performance of GS/TiO2 DSSC is also attributed to the better dye loading of GS/TiO2 film than that of TiO2 film. The effect of GS content on the PV performances was also investigated. It was found that the power conversion efficiency increased first and then decreased with the increasing of GS concentration due to the decrease in the transmittance at high GS content. Further improvements can be expected by fully optimizing fabrication conditions and device configuration, such as increasing dye loading via thicker films. The present synthetic strategy is expected to lead to a family of composites with designed properties.