Enhanced efficiency and stability of dye-sensitized solar cells utilizing FeCo₂S₄ nanowires as Pt-free counter electrodes

Replacing traditional Pt-based counter electrodes with low-cost and highly stable materials is crucial for the development of commercially viable dye-sensitized solar cells (DSSCs). In this study, we synthesized a ternary Pt-free FeCo₂S₄ nanowire (NW)-based sulfide electrocatalyst by a three-step solvothermal method. This material was then used as a counter electrode in DSSCs to facilitate the reduction of triiodide species. The formation of FeCo₂S₄ NW was confirmed by various characterization techniques such as X-ray diffraction, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Scanning electron microscopy analysis revealed the structure of the nanowires. Electrochemical studies, which included cyclic voltammetry, electrochemical impedance spectroscopy and Tafel polarization methods, revealed the excellent stability, superior electrocatalytic activity and remarkable kinetics of FeCo₂S₄ NW in the reduction of triiodide to iodide. Photovoltaic measurements of the fabricated DSSCs yielded a power conversion efficiency (PCE) of 7.88 % for the FeCo₂S₄-based devices, outperforming the control device made of Pt (PCE=7.45 %). This improvement was primarily due to the increase in short-circuit current density (J_SC), thanks to the lower charge transfer resistance (R_CT) of FeCo₂S₄ NW (J_SC=15.23 mA/cm²; R_CT=5.54 Ω cm²) compared to Pt (J_SC=14.12 mA/cm²; R_CT=7.07 Ω cm²). In addition, the FeCo₂S₄ NW-based solar cells exhibited excellent stability and maintained their high PCE value even after 10 days of aging under ambient conditions, while Pt-based DSSCs showed a 3 % decrease from their initial PCE value. This FeCo₂S₄ NW counter electrode proves to be an excellent alternative to Pt, and the presented results provide valuable insights for the development of cost-effective and highly stable DSSCs.