CuFeS₂/Cu₂S/FeS₂ Composite to Increase the Performance of Thin-Film Thermoelectric Generators Based on Sustainable Materials

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