Sustainable sulphides for π-type planar thermoelectric generators

Abstract This study presents the first functioning π-type thermoelectric generator (TEG) constructed exclusively from non-expensive and non-toxic sulphur-based compounds. The TEG comprises spin-coated thin-film legs of p -type Cu₂SnS₃ (CTS, with Cc and F-43 m structures) and n -type Cu 1- x Ag x FeS₂ (CAFS, with I-42d structure). Comprehensive structural and compositional characterization revealed a dense microstructure with nanometric crystallite sizes, which contributes to enhanced device stability and homogeneity. The thermoelectric properties were determined by using a custom-built current–voltage–power apparatus equipped with an automated load resistance ( R load ) switch. The resulting TEG delivered a power output ( P OUT ) of approximately 330 nW per thermocouple, corresponding to a maximum power per unit active planar area of 220 nW cm⁻ 2 at a temperature gradient ( ΔT ) of 170 K. This represents one of the highest performance reported for environmentally friendly sulphide-only thermoelectric TEGs in the medium temperature range. These findings demonstrate the significant potential of CTS and CAFS as scalable, sustainable, economical, and alternative candidates to conventional toxic and costly Te- and Sb-based thermoelectric materials. Graphical abstract