Synergistic Effects Exhibited by the Cobalt Sulfide–Graphitic Carbon Nitride Nanocomposites as Counter Electrodes in Dye‐Sensitized Solar Cells

In the search for a more effective alternative to platinum as a counter electrode (CE) in dye‐sensitized solar cells (DSSCs), we investigated a composite material consisting of cobalt sulfide, a transition metal chalcogenide, and graphitic carbon nitride, a polymeric carbon nitride, aiming to exploit potential synergistic effects for enhanced performance. The CoS/g‐C ₃ N ₄ nanocomposites were synthesized via ultrasonication, while pristine CoS and g‐C ₃ N ₄ were obtained through hydrothermal synthesis and calcination, respectively. Structural and morphological analyses (X‐Ray diffraction, field emission scanning electron microscopy, high‐resolution transmission electron microscopy) confirmed phase purity and revealed distinct nanostructures. Electrochemical characterization in a three‐electrode setup provided insight into their catalytic behaviour, leading to their application as CEs in DSSCs tested under a 1‐sun solar simulator. The nanocomposites exhibited nearly 60% higher performance compared to the individual components, due to their strong synergistic interaction. This translated into a ~19% higher power conversion efficiency than that of the platinum‐based DSSC (7.69%), achieving a maximum efficiency of 9.16% with a short‐circuit current density of 27.2 mA cm ⁻² , an open‐circuit voltage of 701.2 mV, and a fill factor of 0.48. Furthermore, the fabricated cells were studied for the CE stability and device performance over 45 and 90 days.