Contrasting Cu Roles Lead to High Ranged Thermoelectric Performance of PbS

To obtain high-performance PbS-based thermoelectric materials, this study introduces Cu with different contrasting roles in p-type PbS, which can effectively decrease the lattice thermal conductivity and simultaneously optimize the electrical transport properties. Experimental results illustrate that Cu substitutions and Cu interstitials can improve carrier mobility through lowering effective mass (m*) and carrier concentration (n_H) in a low temperature range (300–450 K), and further optimize temperature-dependent n_H in a high temperature range (450–823 K). Both decreased m* and n_H shift the peak power factor to low temperature range, leading to an ultrahigh power factor ≈23 µW cm⁻¹ K⁻² at 423 K for Pb_0.99Cu_0.01S-0.01Cu. Additionally, the special dynamic-doping behaviors of Cu can continuously promote n_H to approach the temperature-dependent relationship of (n_{H, opt}) ≈ (m*T)^1.5, which brings about an eminent average power factor (PF_ave) ≈ 18 µW cm⁻¹ K⁻² among 300–823 K in Pb_0.99Cu_0.01S-0.01Cu. Furthermore, the microstructure characterizations unclose that the atomic and nanoscale Cu-containing defects can effectively intensify the phonon scattering and suppress the lattice thermal conductivity. Consequently, both high ZT (≈0.2 at 300 K) and peak ZT (≈1.2 at 773 K) result in a record-high average ZT (ZT_ave) of ≈0.79 at 300–823 K for Pb_0.99Cu_0.01S-0.01Cu.