Investigations on distinct thermoelectric transport behaviors of Cu in n-type PbS

In this work, we reported the thermoelectric performance of Sb doped n-type PbS can be improved through introducing different types of Cu inclusions (counter-doping, extra-adding and both of them). Firstly, Cu was selected to substitute Pb sites as counter-doping to tune the carrier density, resulting in maintaining power factor but a decreasing total thermal conductivity, thus in a maximum ZT (ZT_max) ∼ 0.96 at 923 K in Pb_0.975Sb_0.02Cu_0.005S. Then, we introduced extra Cu in n-type PbS to form interstitials to further reduce the lattice thermal conductivity to ∼0.77 Wm⁻¹K⁻¹, and the ZT_max was further enhanced to ∼1.06 at 923 K in Pb_0.98Sb_0.02S-0.02Cu. Finally, we combined both types of Cu (counter-doping and extra-adding) into n-type PbS, the power factor experiences slight reduction meanwhile the minimum lattice thermal conductivity can be reduced as low as ∼ 0.57 Wm⁻¹K⁻¹ at 923 K. Combining excellent power factor and dramatically reduced lattice thermal conductivity, we obtained a ZT_max ∼1.23 at 923 K and the ZT_ave ∼0.62 at 300–923 K in Pb_0.95Sb_0.02Cu_0.03S-0.03Cu. This work provides a new idea to improve the thermoelectric performance in n-type PbS, indicating that PbS is one robust alternative of PbTe.