CuFeS<sub>2</sub>/Cu<sub>2</sub>S/FeS<sub>2</sub> Composite\nto Increase the Performance of Thin-Film Thermoelectric Generators\nBased on Sustainable Materials

Thermoelectric devices convert waste heat into electric\nenergy\nbut typically rely on scarce, expensive, and toxic Te-based materials.\nTo address these limitations, we propose the Cu–Fe–S\nsulfide system as a nontoxic, abundant, and environmentally friendly\nalternative, with enhanced properties achieved through the synergistic\nbehavior of CuFeS<sub>2</sub>, Cu<sub>2</sub>S, and FeS<sub>2</sub> phases in a thin-film thermoelectric generator. These phases were\nsynthesized using a three-step process: ball milling, thermal evaporation,\nand sulfurization of Cu/Fe precursors, with the CuFeS<sub>2</sub>/Cu<sub>2</sub>S/FeS<sub>2</sub> phase ratio being tuned by adjusting the\nsulfurization temperature and duration. The presence of binary sulfides\nenhances the electric connectivity between CuFeS<sub>2</sub> grains,\nwhich on their own exhibit poor electrical conductivity due to the\nformation of isolated grains during nucleation. The composite achieved\na volumetric power density of 20 μW cm<sup>–3</sup> K<sup>–1</sup>, outperforming similar Cu-based materials such as\nCu<sub>2</sub>SnS<sub>3</sub> and Cu<sub>2</sub>ZnSnS/Se<sub>4</sub>, mainly due to its optimized phase composition, higher density,\nand the superior Seebeck coefficient and electrical conductivity achieved\nthrough nanoinclusion. The eco-friendly, low-cost Cu–Fe–S\nsystem, synthesized through scalable ball milling and thermal evaporation,\npresents a promising alternative to conventional materials for sustainable\nthermoelectric generation.