Optimizing Dye Adsorption in Graphene–TiO₂Photoanodes for the Enhancement of Photoconversion Efficiency of DSSC Devices

Abstract

We report on the effect of graphene (G) incorporation in TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 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 TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> alone (without graphene). On the other hand, by performing thermogravimetric analyses to quantify the dye adsorption capacity of the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> –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–TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -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.