Quantum‐Dot Sensitized Solar Cells Employing Hierarchical Cu 2 S Microspheres Wrapped by Reduced Graphene Oxide Nanosheets as Effective Counter Electrodes

Hierarchical Cu 2 S microspheres wrapped by reduced graphene oxide (RGO) nanosheets are prepared via a one‐step solvothermal process. The amount of graphene oxide used in the synthesis process has a remarkable effect on the features of Cu 2 S microspheres. Compared to Pt and Cu 2 S electrodes, RGO‐Cu 2 S electrodes show better electrocatalytic activity, greater stability, lower charge‐transfer resistance, and higher exchange current density. As expected, RGO‐Cu 2 S electrodes exhibit superior performance when functioning as counter electrodes in CdS/CdSe quantum dot‐sensitized solar cells (QDSSCs) using a polysulfide electrolyte. A power conversion efficiency up to 3.85% is achieved for the QDSSC employing an optimized RGO‐Cu 2 S counter electrode, which is higher than those of the QDSSCs featuring Pt (2.14%) and Cu 2 S (3.39%) counter electrodes.