An Interconnected Ternary MIn₂S₄ (M=Fe, Co, Ni) Thiospinel Nanosheet Array: A Type of Efficient Platinum‐Free Counter Electrode for Dye‐Sensitized Solar Cells

The ternary iron-group thiospinels of metal diindium sulfides (MIn₂ S₄ , M=Fe, Co, Ni) with a vertically aligned nanosheet array structure are fabricated through an in situ solvothermal method on F-doped tin oxide (FTO) substrates, which are employed as one type of platinum (Pt)-free counter electrodes (CEs) in structure-dependent dye-sensitized solar cells (DSSCs). A DSSC assembled with ternary CoIn₂ S₄ CE achieves an photoelectric conversion efficiency (PCE) of 8.83 %, outperforming than that of FeIn₂ S₄ (7.18 %) and NiIn₂ S₄ (8.27 %) CEs under full sunlight illumination (100 mW cm⁻² , AM 1.5 G), which is also comparable with that of the Pt CE (8.19 %). Putting aside that the interconnected nanosheet array provides fast electron transfer and electrolyte diffusion channels, the highest PCE of CoIn₂ S₄ based DSSC results from its largest specific surface area (144.07 m² g⁻¹ ), providing abundant active sites and the largest electron injection efficiency from CE to electrolyte.