Chemical Pressure-Induced Unconventional Band Convergence Leads to High Thermoelectric Performance in SnTe

Abstract

Band convergence is considered a net benefit to thermoelectric performance as it decouples the density of states effective mass ((Formula presented.)) and carrier mobility (µ) by increasing valley degeneracy. Unlike conventional methods that typically prioritize (Formula presented.) at the expense of µ, this study theoretically demonstrates an unconventional band convergence strategy to enhance both (Formula presented.) and µ in SnTe under pressure. Density functional theory calculations reveal that increasing pressure from 0 to 5 GPa moves the Σ-band of SnTe upward, reducing the energy offset between L- and Σ-band from 0.35 to 0.2 eV while preserving the light band feature of the L-band. Consequently, a high power factor (PF) of 119.2 µW cm−1 K−2 at 300 K is achieved for p-type SnTe under 5 GPa. Chemical pressure also induces conduction band convergence, significantly enhancing the PF of n-type SnTe. Additionally, the interplay between pressure-induced phonon modes leads to a moderate increase in lattice thermal conductivity of SnTe below 3 GPa, which combined with the significantly enhanced PF, contributes to a large enhancement in ZT. Consequently, predicted ZT values of 2.12 at 650 K and 2.55 at 850 K are obtained for p- and n-type SnTe, respectively, showcasing substantial performance enhancements.