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

Abstract 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.