Platinum-free counter electrodes for DSSCs: Emerging materials and synthesis strategies-a review

The growing need for cost-effective and scalable photovoltaic technologies has intensified research on platinum-free (Pt-free) counter electrodes (CEs) for dye-sensitized solar cells (DSSCs). This review examines recent developments across major classes of alternative CE materials, including carbon-based structures, transition-metal sulfides, oxides and nitrides, conductive polymers, metal selenides, and low-cost metals and metal alloys such as Ni, Cu, Ti, and their compounds. The analysis highlights how morphology engineering, heterostructure design, and synergistic material integration improve catalytic activity toward the I₂/I₃⁻ redox couple, electrical conductivity, and long-term stability. Comparative evaluation shows that several Pt-free systems, such as RuS₂/rGO/MWCNTs, Ni- and Co-based sulfides, and selected metal alloy composites, achieve power conversion efficiencies comparable to or exceeding those of Pt-based electrodes, with reported values exceeding 13 % in optimized configurations. Emerging synthesis strategies, including hydrothermal growth, electrochemical deposition, and fabrication of nanostructured composites, further enable high-performance, scalable electrode architectures. Overall, the review identifies key trends driving the advancement of Pt-free CEs and discusses remaining challenges related to electrolyte compatibility, durability, and industrial-scale fabrication, thereby providing a foundation for the future development of sustainable and economically viable DSSC technologies. • Comprehensive review of platinum-free counter electrodes for DSSCs. • Emerging counter electrodes: carbon, sulfides, oxides, nitrides, polymers. • Electrocatalytic properties, stability, and power conversion efficiency. • Tabulated comparison of high-efficiency CE materials from recent studies. • Identified trends and future directions for scalable CE development in DSSCs.