Valence band convergence and nanostructured phonon scattering trigger high thermoelectric performance in SnTe

Abstract

SnTe has recently emerged as a promising alternative to its structurally analogous title holder thermoelectric material PbTe for thermoelectric energy conversion. Herein, we show co-doping of multiple elements to enhance the thermoelectric performance in SnTe via concurrent electronic structure modulation and inhibition of phonon transports. Sb, Mn, and Se co-doped Sn0.7Ge0.3Te results in an optimized p-type carrier concentration and highly converged valence bands, which markedly increases its Seebeck coefficient. The difference in energy between light and heavy hole valence bands (ΔE) reduces to 0.12 eV in Sn0.57Ge0.3Sb0.1Mn0.03Te0.95Se0.05 compared to 0.35 eV for pristine SnTe, which eventually leads to an elevated power factor of ∼27.7 μW/cm K2 at 823 K. In addition, the drastic reduction in the lattice thermal conductivity to a low value of ∼0.57 W/m K at 823 K is obtained for Sn0.57Ge0.3Sb0.1Mn0.03Te0.95Se0.05 due to significant phonon scattering caused by the simultaneous effect of ferroelectric instability and the formation of nanoprecipitates (5–10 nm) in the SnTe matrix. As a synergy among the ultralow lattice thermal conductivity, optimized charge carriers with enhanced valence band convergence, we obtained a high thermoelectric figure of merit, zT of ∼1.35 at 823 K in Sn0.57Ge0.3Sb0.1Mn0.03Te0.95Se0.05.