Enhanced electrocatalytic activity of fluorine and nitrogen-doped graphene oxide as counter electrodes in DSSCs

چکیده مقاله

The development of low-cost and efficient counter electrodes is essential for reducing the dependence of dye-sensitized solar cells (DSSCs) on platinum (Pt). In this work, pristine graphene oxide (GO), fluorine-doped graphene oxide (FGO), and nitrogen/fluorine co-doped graphene oxide (NFGO) were investigated as counter-electrode materials for the iodide/triiodide redox couple, with conventional Pt used as a reference. Structural and surface characterization by SEM/EDX, BET, XRD, XPS, and FTIR confirmed substantial modification of the GO framework following heteroatom incorporation. Among the investigated materials, FGO exhibited the most favorable morphology, with a highly porous and branched structure and the largest BET specific surface area of 354.85 m² g⁻¹, compared with 185.98 m² g⁻¹ for NFGO and 67.52 m² g⁻¹ for GO. XPS further confirmed fluorine incorporation through semi-ionic and covalent C–F bonding configurations. Cyclic voltammetry showed that FGO produced the highest cathodic peak current density of 0.354 mA cm⁻², compared with 0.307 mA cm⁻² for Pt, while exhibiting an essentially identical peak-to-peak separation to Pt, indicating a strong overall electrocatalytic response toward the I⁻/I₃⁻ redox reaction. Symmetric-cell electrochemical impedance spectroscopy revealed comparable counter-electrode charge-transfer resistances for FGO (25.94 Ω) and Pt (26.46 Ω), whereas substantially higher values were obtained for NFGO and GO. In complete DSSCs, FGO exhibited reduced interfacial resistances and delivered the highest photovoltaic performance, with a power conversion efficiency of 9.59%, a short-circuit current density of 19.30 mA cm⁻², an open-circuit voltage of 0.73 V, and a fill factor of 69%, compared with 8.64% efficiency for the Pt-based device. The enhanced performance of FGO is attributed to the combined effects of its highly accessible porous structure, fluorine-induced modification of the electronic and bonding environment, and favorable electrode/electrolyte interfacial charge transfer. These findings demonstrate the potential of fluorine-functionalized graphene oxide as a Pt-free counter-electrode material for high-performance DSSCs.