CoS nanosheets-coupled graphene quantum dots architectures as a binder-free counter electrode for high-performance DSSCs

Hybrid materials with alternate components and synergetic effects are promising and intriguing materials as electrodes for high-performance energy storage/conversion devices. Cobalt sulphide (CoS) is one of the low-cost but inactive catalysts as counter electrode (CE) for dye-sensitized solar cells (DSSCs). How to optimize its structure and further enhance its electrochemical activity for I-3(-) reduction remains a major challenge. Herein, a simple and efficient approach has been adopted to configure CoS sheets-coupled graphene quantum dots (GQDs) architectures via electrodepositing GQDs and CoS on the fluorine doped tin oxide glass substrate. When employed as the binder-free CE for DSSCs, the as-made CoS-GQDs exhibits a high catalytic activity towards the reduction of I-3(-), evidenced by the results of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements. A conversion efficiency of 7.30% is achieved, being superior to CoS CE (5.55%) and Pt CE (6.94%) due to their synergetic effects. The present work provides a simple method for configuring low-cost binder-free CE materials for replacing Pt.