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

Abstract

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 Cu_2−xSe/Cu₇S₄ nanoboxes (DW-Cu_2−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-Cu_2−xSe/Cu₇S₄-HNB CE, which is inclusively derived from the high intrinsic electron conductivity of Cu_2−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-Cu_2−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-Cu_2−xSe/Cu₇S₄-HNB CE still shows superior long-term stability towards the polysulfide electrolyte even after 600 cycles.