Double-walled heterostructured Cu2-xSe/Cu7S4 nanoboxes with enhanced electrocatalytic activity for quantum dot sensitized solar cells

It is of great importance to develop counter electrodes (CEs) as an alternative for enhancing the power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSSCs). Here, single-walled Cu7S4 nanoboxes (SW-Cu7S4-NBs) and double-walled heterostructured Cu2-xSe/Cu7S4 nanoboxes (DW-Cu2-xSe/Cu7S4-HNBs) are synthesized by a facile in situ inward etching/sacrificial template method based on the Kirkendall effect. A remarkably enhanced and stable electrocatalytic activity is achieved for the QDSSC based on the DW-Cu2-xSe/Cu7S4-HNB CE, which is inclusively derived from the high intrinsic electron conductivity of Cu2-xSe, the stimulated electron transfer process and abundant active catalytic sites due to the enlarged specific surface area, higher utilization efficiency of incident light of the unique double-walled hollow structure, and the formation of a heterogeneous nanostructure. As a result, the QDSSC based on the DW-Cu2-xSe/Cu7S4-HNB CE exhibits a PCE of 4.38% under 1 sun (100 mW cm(-2)) irradiation, while 3.97%, 3.43% and 1.54% were found for SW-Cu7S4-NB, Pt and brass/Cu2S based CEs, respectively. Furthermore, it is suggested that the DW-Cu2-xSe/Cu7S4-HNB CE still shows superior long-term stability towards the polysulfide electrolyte even after 600 cycles.