Novel method for synthesis of reduced graphene oxide–Cu2S and its application as a counter electrode in quantum-dot-sensitized solar cells

Reduced graphene oxide (rGO)-Cu2S as a counter electrode (CE) is synthesized by a novel electrochemical method for quantum-dot-sensitized solar cell (QDSSC) applications. One-step electrochemical co-reduction using cyclic voltammetry for various cycles (3, 5, and 7), followed by sulfurization, is employed to obtain rGO-Cu2S CEs on the surface of fluorine-doped tin oxide. Compared with Pt and Cu2S CEs, rGO-Cu2S CEs (5) display lower charge transfer resistance (Rct) and higher electrocatalytic activity. This is because the introduction of rGO along with Cu2S in the rGO-Cu2S surface enhances the surface area and charge transfer and improves the electrical contact between the CEs and substrate surface. An optimum power conversion efficiency (η) of 4.26% is recorded for rGO-Cu2S (5) in CdS/CdSe/ZnS QDSSCs using a polysulfide electrolyte. QDSSCs with rGO-Cu2S (5) showed the highest short-circuit current density (Jsc) of 17.2 mA cm−2, open circuit voltage (Voc) of 0.57 V, and fill factor of 44%. The obtained results are superior to those for Cu2S (3.77%) and Pt (2.44%) CEs. Additionally, the preparation method of rGO-Cu2S CEs is more scientific, less time-consuming, economical, and easy.