Graphene–anthocyanin mixture as photosensitizer for dye-sensitized solar cell

• Anthocyanin dye co-adsorbed with graphene increased DSSC power conversion efficiency.
• Impedance spectroscopy reveals decreased charge transfer resistances with graphene added.
• 2.4-Fold increase in efficiency was obtained with graphene added to dye and titania.

In this study, enhancement in efficiency of anthocyanin-based dye sensitized solar cells (DSSC) through the incorporation of graphene directly into the dye mixture is demonstrated. Graphene was incorporated in the anthocyanin dye mixture and allowed to co-adsorb on the mesoporous titania; this is compared with anthocyanin-only mixture as control, and also compared with DSSC with graphene incorporated directly into the titania. Current–voltage (IV) and electrochemical impedance spectroscopy (EIS) measurements were carried out to characterize the different DSSC cells. Addition of graphene resulted in increased power conversion efficiencies: addition into the TiO2 as a photoanode composite, direct addition to the anthocyanin extracts (anthocyanin:graphene dispersion) during the adsorption step, or a combination of these two. The latter resulted in the highest enhancement in the PCE by as much as 2.4 times. EIS data showed a favorable decrease in charge transfer resistance in the TiO2 layer as graphene is added to the DSSC, with increased magnitude of the short-circuit current (Jsc). This is explained by graphene providing added conducting pathways for the photo-generated electrons; results show that this is also manifested in the co-adsorption of graphene with the anthocyanin dye onto the titania anode.