Effect of Graphene/TiO₂ Composite Layer on the Performance of Dye-Sensitized Solar Cells

Graphene has attracted a lot of attention because of its unique mechanical, thermal, electrical and optical properties. In this study, a double layered structured photoanode consisting of a graphene/TiO2 composite layer and a TiO2 nanoparticles (P25) underlayer was developed. The photoelectric properties of as-prepared double layer structured photoanode were studied with comparison of the anatase TiO2 photoanode. Graphene was prepared by reduction of graphene oxide (GO) under a hydrothermal conditions and graphenen/TiO2 composite semiconductor materials were prepared by mixing graphene into TiO2 paste. The effect of graphene contents in graphene/TiO2 composite layer was also investigated. After constructing double layer photoanode with proper amount of graphene, the photoanode displayed enhanced light and dye adsorption properties with higher light harvesting efficiency, lower internal resistances, faster electron transport and lower charge recombination rate, which resulted in high current density. At the optimum conditions, the DSSC exhibited a Jsc of 15.01 mA cm-2, a Voc of 0.72 V, and a FF of 0.66 with the energy conversion efficiency (η) of 7.08%, indicating a increase in Jsc and η respectively than that of DSSC based on pure TiO2 photoanode, which gives a Jsc of 13.25 mA cm-2, a Voc of 0.73 V, and a FF of 0.62 with a η of 5.94%. However, the addition of excess graphene in the composite layer led to the enhancement of charge recombination, the reduction of dye adsorption and the decrease of photoelectric conversion efficiency of DSSCs. The graphene/TiO2 composite layer in DSSCs could really enhance its efficiency after the amount of graphene was successfully optimized.