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 CuFeS2, Cu2S, and FeS2 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 CuFeS2/Cu2S/FeS2 phase ratio being tuned by adjusting the sulfurization temperature and duration. The presence of binary sulfides enhances the electric connectivity between CuFeS2 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 Cu2SnS3 and Cu2ZnSnS/Se4, 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.