Synthesis of highly active cobalt molybdenum sulfide nanosheets by a one-step hydrothermal method for use in dye-sensitized solar cells

Cobalt molybdenum sulfide (Co(1 - x)MoxS2, x = 2/3, 1/2, 1/3) nanocomposites with hierarchical nanosheet structure are prepared on the flexible titanium foils by a facile hydrothermal method and used as the counter electrode (CE) materials for the dye-sensitized solar cells (DSSCs). It is interesting that the first produced MoS2 nanosheets play an important role as the template for the continuously growing of the Co(1 - x)MoxS2 nanosheets. Otherwise, it will grow up into octahedral CoS2 in the synthesis system without the Mo source. The Co(1 - x)MoxS2 CE demonstrates higher catalytic activity for the reduction of triiodide to iodide than that of the MoS2, and CoS2 CEs due to the Co(1 - x)MoxS2 CE with thinner hierarchical nanosheets offers more catalytic active sites and exhibits additional synergistic effect of the combination of Mo and Co. The DSSC with Co1/2Mo1/2S2 CE achieves a photovoltaic conversion efficiency of 9.16%, which is higher than that of the MoS2 (8.27%) and CoS2 (7.18%) CEs and even higher than that of the platinum CE (8.49%) under full sunlight illumination (100 mW cm(-2), AM 1.5 G).