Enhanced thermoelectric performance in Sb-Br codoped Bi2Se3 with complex electronic structure and chemical bond softening.

Ju Zhang,Shiqi Zhong,San-Huang Ke

doi:10.1039/d1ra08726f

Abstract

Prior experimental work showed that Bi2Se3, as a sister compound of the best room-temperature thermoelectric material Bi2Te3, has remarkably improved thermoelectric performance by Sb–Br codoping. But the relationship between its crystalline structure and thermoelectric properties is still unclear to date. Here, we use first-principles calculations to explore the possible reasons for such improvement. The electronic structures of Bi2−xSbx(Se1−yBry)3 (x = 0, 1, 2; y = 0, 0.08) are systematically investigated. Significant effects of 8% Br codoping in BiSbSe3 are found. First, the Br atom acts as an electron donor, thus greatly increasing the carrier concentration. Second, similar to the effect of Sb doping, Br codoping further improves greatly the degeneracy of the conduction band edge, which leads to a remarkably increased density-of-states effective mass without deterioration of the carrier mobility, and simultaneously preserves a large Seebeck coefficient of ∼−254 μV K−1 at 800 K. In addition, the Br codoping softens the chemical bonds, which enhances anharmonic scattering and further reduces the lattice thermal conductivity. We predict that the maximum zT of BiSb(Se0.92Br0.08)3 at 800 K can reach 0.96 with the carrier concentration of 9.22 × 1019 cm−3. This study rationalizes a potential strategy to improve the thermoelectric performance of Bi2Se3-based thermoelectric materials.

Highlights

With about two-thirds of the world's produced energy being lost as waste heat,[1] thermoelectric (TE) materials which can directly convert exhaust heat into usable electricity have been investigated widely as clean and sustainable energy materials.[2]
The distinct layered structure consists of a regular octahedron structure with Bi atom as the center and Se atom as the vertex
The residual stress is set to be less than 0.1 GPa

Summary

Introduction

With about two-thirds of the world's produced energy being lost as waste heat,[1] thermoelectric (TE) materials which can directly convert exhaust heat into usable electricity have been investigated widely as clean and sustainable energy materials.[2]. It is well known that the electrical transport properties of a material are dominated by the details of its band structure and the combination of all these features has been identi ed[12,15] with a large challenge in achieving high-performance thermoelectrics through an avenue simultaneously possessing large band degeneracy and strong anharmonic lattice dynamics, which are highly inter-dependent. As the best commercialized thermoelectric material found so far, Bi2Te3 has excellent s, S, and large zT (for both n-type and p-type), and have been widely applied for TE power generation and electronic cooling around room temperature.[16] Te is a scarce element in the crust of the earth and its cost would rise

Methods

Results

Conclusion