Platinum counter electrodes are a critical component of dye-sensitized solar cells (DSSCs). They regenerate the I₃⁻/I⁻ redox electrolyte. However, the expense and rarity of platinum threaten the commercial viability of DSSCs.

In a search for cheaper alternatives, Yaoming Xiao, Gaoyi Han, and colleagues, Shanxi University, Taiyuan, China, have used an in situ solvothermal method to fabricate porous nanosheet arrays of ternary thiospinels (MIn₂S₄; M = Fe, Co, Ni) on conducting fluorine-doped tin oxide. The material offers abundant active sites for I₃⁻ reduction, channels for rapid electrolyte transport and charge transfer, and appropriate energy level alignment at the electrode interface.

A CoIn₂S₄ counter electrode with a large 144.07 m²g^–1 specific surface area reached an 8.83 % photoelectric conversion efficiency in full sunlight, which rivals that of platinum. The researchers believe MIn₂S₄ could replace platinum electrodes in other electrocatalytic applications. The compounds could also possibly be used in wearable devices because they can be prepared on flexible substrates.

• An Interconnected Ternary MIn₂S₄ (M=Fe, Co, Ni) Thiospinel Nanosheet Array: A Type of Efficient Platinum-Free Counter Electrode for Dye-Sensitized Solar Cells,
  Wenjing Hou, Yaoming Xiao, Gaoyi Han,
  Angew. Chem. Int. Ed. 2017.
  DOI: 10.1002/anie.201705399