Synergistic band modulation and phonon suppression to improve PbBi2S4 thermoelectric performance
Abstract
PbBi2S4 has emerged as a promising thermoelectric material due to its distinctive layered structure and low thermal conductivity. However, its practical applications are hindered by suboptimal electrical transport properties, and engineering the complex electronic band structure derived from the layered lattice is crucial to addressing this challenge. This study presents a dual-approach optimization strategy involving Sb doping and Se alloying to synergistically improve the electrical and thermal properties of PbBi2S4. First, Sb as an aliovalent dopant regulates carrier density to optimize charge transport, while Sb incorporation induces conduction band flattening. Hence, Sb doping simultaneously enhances both the electrical conductivity (increasing carrier density) and Seebeck coefficient (band flattening), which manifests in a nearly doubled weighted mobility (μw) at room temperature, leading to substantial improvement in electrical performance (power factor). Then, Se alloying further suppresses the lattice thermal conductivity (κlat) to 0.27 W m−1 K−1 through enhanced phonon scattering, while maintaining optimized charge transport. The ratio of weighted mobility to lattice thermal conductivity (μw/κlat), a comprehensive indicator of thermoelectric performance, is significantly enhanced to ∼2.3 times at 300 K and ∼2.2 times at 773 K that of pure PbBi2S4. The charge and phonon transport mechanisms underlying the thermoelectric enhancement are well elucidated by the theoretical band structure calculations and microstructure characterization. Finally, a maximum ZT value of 0.78 is achieved in Pb0.91Sb0.09Bi2S3.95Se0.05, representing ∼1.7 times improvement over the pristine PbBi2S4, making it one of the most competitive ternary S-based compounds.