Realizing high thermoelectric performance in copper sulfide via intermediate doping

• • The optimal composition Cu1.8S + 5 wt.% bronze + 3 wt.% cupronickel + 2 wt.% brass achieves a ZT of 1.7 at 673 K, a 247% enhancement over pristine Cu1.8S, surpassing all previously reported ZT values for the Cu1.8S system. • • Intermediate doping with copper alloys increases the solubility limits of Zn, Sn, Pb, and Ni, enabling optimized carrier concentration and enhanced electrical conductivity without compromising the Seebeck coefficient. • • In situ formation of nanoscale second phases effectively scatters phonons, reducing lattice thermal conductivity, with the dual synergistic mechanism of electronic and thermal transport optimization. • • The intermediate doping strategy outperforms conventional direct elemental doping, providing a new route for optimizing thermoelectric performance in copper sulfide and potentially other alloy-based thermoelectric systems.