MXene/NiCo₂S₄ 2D/3D Heterostructure as a High-Performance Pt-Free Counter Electrode for DSSCs

This study represents a novel 2D/3D heterostructure of MXene/NiCo₂S₄ composites, which were used for the first time as a high-performance counter-electrode material for Pt-free dye-sensitized solar cells (DSSCs). The unique morphology of 2D-MXene/3D-NiCo₂S₄ proved advantageous in producing good electrode/electrolyte interfacial contact, enhancing the electrocatalytic activity via vigorous electron transfer and ion diffusion. Cyclic voltammetry, Tafel polarization, and electrochemical impedance spectroscopy measurements confirmed that hierarchical interconnection and aggregation of 2D-MXene sheets/3D-NiCo₂S₄ nanoparticles lead to both fast charge transport and rapid redox reaction kinetics. Consequently, the DSSC device assembled with the 2D-MXene/3D-NiCo₂S₄ counter electrode exhibited a higher photovoltaic conversion efficiency of up to 8.76 % compared to that of the standard Pt counter electrode-assembled device (8.46 %). These findings offer a perspective design concept for materializing the Pt-free, high-performance 2D/3D hierarchical heterostructure as a superb counter electrode of next-generation photovoltaic devices.