Bi-addition improves the thermoelectric performance of InSb

Abstract

Owing to advanced characteristics of a narrow bandgap, high electron mobility, and abundant raw material resources, InSb has been considered as a promising environmental-friendliness thermoelectric material. However, its thermoelectric performance remains unsatisfactory because of its low initial carrier concentration, low electrical conductivity, and high thermal conductivity. Here, we use Bi addition to enhance the thermoelectric performance of InSb. Bi plays two critical roles for the enhanced performance: substituting Sb and forming Bi-rich secondary phase at grain boundaries. First-principles calculations show that Bi_Sb causes the Fermi level to shift into the conduction band, which increases carrier concentration and electrical conductivity. Meanwhile, the enrichment and precipitation of Bi at grain boundaries forms heterogeneous phase boundaries, which induces an energy filtering effect to enhance the Seebeck coefficient and a high power factor of 56.1 μW cm⁻¹ K⁻² at 693 K for the InSb_0.97Bi_0.03, about 42 % higher than that of intrinsic InSb. Additionally, the formation of Bi_Sb point defects and the additional phonon scattering caused by the precipitated phase at grain boundaries result in a reduction in lattice thermal conductivity, collectively resulting in a maximum ZT value of 0.6 at 693 K, approximately 38 % higher than that of intrinsic InSb. Furthermore, the as-fabricated single-leg thermoelectric device based on InSb_0.97Bi_0.03 achieves an output power of 554 nW under a temperature difference of 395 K, indicating considerable application potential.