Cu₂S Reduced Graphene Oxide Composite for High-Efficiency Quantum Dot Solar Cells. Overcoming the Redox Limitations of S₂–/Sn²– at the Counter Electrode

Polysulfide electrolyte that is employed as a redox electrolyte in quantum dot sensitized solar cells provides stability to the cadmium chalcogenide photoanode but introduces significant redox limitations at the counter electrode through undesirable surface reactions. By designing reduced graphene oxide (RGO)-Cu₂S composite, we have now succeeded in shuttling electrons through the RGO sheets and polysulfide-active Cu₂S more efficiently than Pt electrode, improving the fill factor by ∼75%. The composite material characterized and optimized at different compositions indicates a Cu/RGO mass ratio of 4 provides the best electrochemical performance. A sandwich CdSe quantum dot sensitized solar cell constructed using the optimized RGO-Cu₂S composite counter electrode exhibited an unsurpassed power conversion efficiency of 4.4%.