Optimization of Thermoelectric Performance in p-Type SnSe Crystals Through Localized Lattice Distortions and Band Convergence

Crystalline thermoelectric materials, especially SnSe crystals, have emerged as promising candidates for power generation and electronic cooling. In this study, significant enhancement in ZT is achieved through the combined effects of lattice distortions and band convergence in multiple electronic valence bands. Density functional theory (DFT) calculations demonstrate that cation vacancies together with Pb substitutional doping promote the band convergence and increase the density of states (DOS) near the Fermi surface of SnSe, leading to a notable increase in the Seebeck coefficient (S). The complex defects formed by Sn vacancies and Pb doping not only boost the Seebeck coefficient but also optimize carrier concentration (n_H) and enhance electrical conductivity (σ), resulting in a higher power factor (PF). Furthermore, the localized lattice distortions induced by these defects increase phonon scattering, significantly reducing lattice thermal conductivity (κ_lat) to as low as 0.29 W m^-1 K^-1at 773 K in Sn_0.92Pb_0.03Se. Consequently, these synergistic effects on phonon and electron transport contribute to a high ZT of 1.8. This study provides a framework for rational design of high-performance thermoelectric materials based on first-principles insights and experimental validation.