An Interconnected Ternary MIn2 S4 (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.