Fe_1-xCo_xS₂ Solid Solutions with Tunable Energy Structures to Enhance the Performance of Triiodide Reduction in Dye-Sensitized Solar Cells

The electrocatalytic performances of semiconductors are closely correlated to their energy structures, and solid solutions can continuously tune the energy structures by controlling their composition. Herein, a series of Fe_1-xCo_xS₂ (x=0–0.5) solid solutions have been synthesized and served as counter electrodes in dye-sensitized solar cells (DSSCs). The Fermi level of Fe_1-xCo_xS₂ solid solutions shifted negatively as the x value changed from 0 to 0.5, and the electrocatalytic performance for I₃ ⁻ reduction gradually enhanced due to the facilitated electron transfer process from electrode to I₃ ⁻. Benefitting from its negative Fermi level, Fe_0.5Co_0.5S₂ exhibited the smallest charge transfer resistance (R_ct) and remarkable electrocatalytic properties. The DSSCs using Fe_0.5Co_0.5S₂ as a counter electrode achieve the lowest R_ct (0.84 Ω cm²) and the highest power conversion efficiency (η=8.36%) of these solid solution materials.