Optimizing Dye Adsorption in Graphene–TiO$_2$ Photoanodes for the Enhancement of Photoconversion Efficiency of DSSC Devices

We report on the effect of graphene (G) incorporation in TiO2 photoanodes (PAs) for improving their dye adsorption capacity, which in turn impacts the overall photoconversion efficiency of dye-sensitized solar cells (DSSCs). By varying the graphene content of TiO2 PAs (over the 0.05–1 wt.% range), the power conversion efficiency (PCE) of the DSSCs was found to increase significantly from 3.0% for standard TiO2 to a maximum value of 8.2% for PAs containing 0.1 wt. % of graphene. This corresponds to a PCE improvement of ∼173% in comparison with standard DSSCs made with TiO2 alone (without graphene). On the other hand, by performing thermogravimetric analyses to quantify the dye adsorption capacity of the TiO2–G PAs, we were able to establish, for the first time, a direct correlation between the PCE of the DSSCs and the dye uptake of their G–TiO2-based PAs. Our results demonstrate that by coupling the optimal PA (with the optimal graphene content of 0.1 wt.% and optimal sensitization with a solution of 4 mM of N719) with Co–Ni nanoparticles decorated multi-walled carbon nanotubes (MWCNTs) based counter electrodes, we were able to achieve DSSCs exhibiting a PCE as high as 9.8%. This performance is quite impressive particularly considering that no platinum was used in the counter electrode.