Pompon-like NiCo2O4 nanospheres: a potential candidate for the counter electrode in quantum dot-sensitized solar cells

To find a novel counter electrode (CE) material for quantum dot-sensitized solar cells (QDSSCs), pompon-like NiCo2O4 nanospheres are synthesized by a facile solvothermal and post-calcination method and we attempt to apply it as a CE material for QDSSC. The catalytic performance of NiCo2O4 counter electrode is investigated in detail through electrochemical impedance spectroscopy, Tafel test and cyclic voltammetry. The catalytic activity of NiCo2O4 CE is superior to that of nanoflower-like Cu2S CE and traditional Cu2S/brass CE, which is mainly attributed to the large specific surface area, outstanding electrical conductivity of bimetallic oxides and the synergistic promotion effect of metals with different valence states. Under standard sunlight (air mass AM 1.5G 100 mW center dot cm(-2)), the CdS/CdSe/ZnS-sensitized solar cell assembled with NiCo2O4 CE achieved a photoelectric conversion efficiency of 5.55%, with a short current density of 22.49 mA center dot cm(-2), an open circuit voltage of 0.574 V, and a fill factor of 0.43, which is slightly higher than the QDSSCs with nanoflower-like Cu2S CE (4.75%) and traditional Cu2S/brass CE (4.69%). This research provides ideas for discovering innovative and efficient CE materials for QDSSCs.