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 J _sc of 15.01 mA cm⁻², a V _oc of 0.72 V, and a FF of 0.66 with the energy conversion efficiency (η) of 7.08%, indicating a increase in J _sc and η respectively than that of DSSC based on pure TiO₂ photoanode, which gives a J _sc of 13.25 mA cm⁻², a V _oc 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.