Development of binary transition metallic selenide (NiSe/Co₃Se₄) hybrid counter electrode for highly efficient Pt-free dye-sensitized solar cells

Pt-free dye-sensitized solar cells (DSSCs) have emerged as cost-effective alternatives in energy storage technologies, attracting considerable research interest over the past two decades. In this study, we successfully fabricated a NiSe/Co₃Se₄ hybrid counter electrode (CE) using a facile ultrasonic-assisted hydrothermal method, demonstrating its potential for enhancing the performance and stability of DSSCs. X-ray diffraction (XRD) investigation showed hexagonal NiSe and monoclinic Co₃Se₄ phases in the composite, with smaller crystallite sizes indicating better interfacial contacts. SEM and TEM micrographs show a well-defined nanostructure with spherical NiSe particles and rod-like Co₃Se₄ particles. This results in a large surface area and improved porosity, as validated by BET analysis. Electrochemical studies, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization, show that the NiSe/Co₃Se₄ composite has superior electro catalytic activity compared to individual NiSe and Co₃Se₄ electrodes, closely matching the performance of the Pt electrode. When integrated into DSSCs, the NiSe/Co₃Se₄ composite CE obtained an energy conversion efficiency of 9.01%, with notably enhanced short-circuit current density (J_sc) and open-circuit voltage (V_oc). The NiSe/Co₃Se₄ combination is a good contender for large-scale DSSC applications due to its strong photovoltaic performance and stability over 42 days under one-sun illumination.