Realizing high thermoelectric performance in copper sulfide via intermediate doping
Copper sulfide (Cu2−xS) is a low-cost, eco-friendly thermoelectric material, but its performance is limited by the trade-off between electrical conductivity and thermal conductivity. This study introduces an intermediate doping strategy using copper alloys (bronze, cupronickel, brass) to partially replace the copper source in Cu1.8S, addressing excessive Cu vacancies. The approach enhances the solubility limits of Zn, Sn, Pb, and Ni, optimizing carrier concentration, and generates in situ nanoscale second phases that scatter phonons. 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% improvement over pristine Cu1.8S and the highest reported for this system. This work establishes intermediate doping as a viable paradigm for optimizing thermoelectric properties in alloy-based systems.