Soft functionalization of graphene for enhanced tri-iodide reduction in dye sensitized solar cells

Anchoring functional moieties on the surface of graphene is an important step in the processing of graphene for numerous applications. In this article, the effects of two different functionalization methods on graphene viz. the conventional method involving ultrasonication in acids and a novel polyelectrolyte based method are systematically investigated. While the conventional acid treatment method makes graphene highly hydrophilic, it also causes severe damage to the graphene sheets and leads to disordered restacking. In contrast, the soft functionalization method based on polyelectrolytes preserves the morphology to a significant extent. Moreover, the presence of charges on the surface of polyelectrolyte modified graphene causes mutual repulsion between the sheets, thereby assisting in the fabrication of optically transparent films. The presence of charges also affects the electrochemical behaviour towards tri-iodide reduction, which is investigated via electrochemical impedance spectroscopy. New equivalent circuits are proposed to interpret the observed response.