Phase Boundary Metallization Enables Electron‐Phonon Transport Decoupling in PbS‐Based Thermoelectric

Lead sulfide (PbS) is a promising mid‐temperature thermoelectric material, but its performance is constrained by high lattice thermal conductivity ( κ lat ) and relatively low carrier mobility. Traditional construction of nanoscale second phases can effectively suppress κ lat , but severely impairs carrier mobility. Herein, phase boundary metallization is engineered to simultaneously achieve the electron‐phonon transport decoupling in PbS. Specifically, through substantial Cu introduction and Te substitution, the metallic Cu‐enriched phase bridges the PbS matrix and the low‐miscibility PbTe phase at the grain boundary, thereby forming a metallized Cu semi‐coherent interface. Microstructural characterization has further confirmed that massive Cu accumulation at the grain boundaries forms semi‐coherent phase interfaces, which serve as fast channels for carrier transport while enhancing phonon scattering at the interfaces. Therefore, this strategy not only increases carrier mobility to ≈1037 cm 2 V −1 s −1 , but also significantly reduces lattice thermal conductivity to ≈0.85 W m −1 K −1 at 300 K in PbS 0.6 Te 0.4 ‐1.4%Cu sample. Ultimately, a room‐temperature ZT of 0.37 and an average ZT of 0.70 (300–773 K) are achieved, with a measured 5.5% conversion efficiency at Δ T = 408 K. This approach of decoupling electron‐phonon transport via phase boundary metallization provides new perspectives for developing high‐performance thermoelectrics.