Enhanced thermoelectric performance in high-defect SnTe alloys: a significant role of carrier scattering

Abstract

High-level alloying is an effective approach to achieve high thermoelectric performance of SnTe-based materials with high intrinsic defects and poor band structure, but higher concentrations of defects severely deteriorate mobility and lead to erroneous assessment of carrier transport by conventional electrical models. Here, we introduce sufficient Sb₂Te₃ and Cd into the SnTe matrix to generate more vacancies, and further analyze the possible carrier scattering mechanism and performance tuning. As a result, the synergistic effect of Sb₂Te₃ and Cd optimizes the band structure and reintegrates the multivalent band transport. The quantified carrier scattering mechanism dominated by alloy scattering and ionized impurity scattering rationally explains the mobility degradation after heavy doping, and confirms a higher optimal carrier concentration of ∼10²⁰ cm⁻³ in convergent SnTe materials. Furthermore, the vacancies and substitution defects trigger more lattice disorder, which further scatters phonons and leads to low lattice thermal conductivity. Consequently, a peak zT of ∼1.3 (at 753 K) and a remarkable average zT of ∼0.87 (303–853 K) are achieved in the Sn_0.94Cd_0.06Te-0.08Sb₂Te₃ sample. This work is instructive for the decoupling and optimization of highly defective SnTe-based electron–phonon transport, and provides an effective strategy for potential applications in other thermoelectric materials.