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

Band convergence is considered a net benefit to thermoelectric performance as it decouples the density of states effective mass ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>m</mml:mi> <mml:mi>d</mml:mi> <mml:mo>∗</mml:mo></mml:msubsup> <mml:annotation>$m_{\mathrm{d}}^{\mathrm{*}}$</mml:annotation></mml:semantics> </mml:math> ) and carrier mobility (µ) by increasing valley degeneracy. Unlike conventional methods that typically prioritize <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>m</mml:mi> <mml:mi>d</mml:mi> <mml:mo>∗</mml:mo></mml:msubsup> <mml:annotation>$m_{\mathrm{d}}^{\mathrm{*}}$</mml:annotation></mml:semantics> </mml:math> at the expense of µ, this study theoretically demonstrates an unconventional band convergence strategy to enhance both <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>m</mml:mi> <mml:mi>d</mml:mi> <mml:mo>∗</mml:mo></mml:msubsup> <mml:annotation>$m_{\mathrm{d}}^{\mathrm{*}}$</mml:annotation></mml:semantics> </mml:math> 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.