Enhancing Thermoelectric Properties of n-Type PbS through Band Convergence and Defect Modulation via CuFeS2 Alloying

Lead sulfide (PbS) stands out as a compelling candidate for mid-temperature thermoelectric energy conversion owing to its earth abundance and cost-effectiveness. However, its practical application is severely constrained by the intrinsic coupling between electrical and thermal transport parameters, which precludes simultaneous enhancement of the Seebeck coefficient and electrical conductivity. Herein, we report a synergistic strategy of CuFeS2 alloying in Cl-doped PbS that effectively decouples these competing parameters through concurrent band convergence and defect modulation. First, acting as electron acceptors, Cu and Fe precisely adjust the carrier concentration and substantially increase the room-temperature carrier mobility to 312 cm2 V–1 s–1, corresponding to a ∼160% enhancement relative to the pristine PbS0.98Cl0.02 reference sample. Second, the electronic band structure calculations reveal that Cu and Fe doping significantly reduces the energy offset between the two conduction band valleys, promoting multi-band degeneracy that effectively increases the density-of-states effective mass and the Seebeck coefficient. Additionally, the abundant point defects, dislocations, and nanoprecipitates induced by alloying act as efficient phonon scattering centers, reducing the lattice thermal conductivity. Consequently, a superior zT value of ∼1.0 and an average zT (zTave) of ∼0.49 are achieved in the PbS0.98Cl0.02 + 3% CuFeS2 sample. This work demonstrates the decoupling of electron–phonon transport in PbS and offers a broadly applicable alloying strategy for developing high-performance, low-cost thermoelectric materials.