Biaxial Tensile Strain-Induced Enhancement of Thermoelectric Efficiency of α-Phase Se2Te and SeTe2 Monolayers.

Shao-Bo Chen,Gang Liu,Cui-E Hu,Xiang-Rong Chen,Wan-Jun Yan,Hua-Yun Geng

doi:10.3390/nano12010040

Abstract

Thermoelectric (TE) materials can convert waste heat into electrical energy, which has attracted great interest in recent years. In this paper, the effect of biaxial-tensile strain on the electronic properties, lattice thermal conductivity, and thermoelectric performance of α-phase Se2Te and SeTe2 monolayers are calculated based on density-functional theory and the semiclassical Boltzmann theory. The calculated results show that the tensile strain reduces the bandgap because the bond length between atoms enlarges. Moreover, the tensile strain strengthens the scatting rate while it weakens the group velocity and softens the phonon model, leading to lower lattice thermal conductivity kl. Simultaneously, combined with the weakened kl, the tensile strain can also effectively modulate the electronic transport coefficients, such as the electronic conductivity, Seebeck coefficient, and electronic thermal conductivity, to greatly enhance the ZT value. In particular, the maximum n-type doping ZT under 1% and 3% strain increases up to six and five times higher than the corresponding ZT without strain for the Se2Te and SeTe2 monolayers, respectively. Our calculations indicated that the tensile strain can effectively enhance the thermoelectric efficiency of Se2Te and SeTe2 monolayers and they have great potential as TE materials.

Highlights

Thermoelectric materials have drawn considerable attention because they can harvest energy from waste heat by converting thermal energy directly into electrical energy [1,2,3].The conversion efficiency of a TE material can be evaluated by the dimensionless figure of merit, ZT = S2 σT/(k e + k l ), where S, σ, T are the Seebeck coefficient, the electrical conductivity, and the absolute temperature, respectively. ke and kl are electronic and lattice thermal conductivities
The top and side views of the α-phase Se2 Te and SeTe2 monolayers are shown in Generally speaking, it is vital to check the stability of materials before calculating the properties
The longitudinal acoustic (LA) and transverse acoustic (TA) branches are linear near the Γ point, while the out-of-plane acoustic (ZA) branch is quadratic near the Γ point, and all of them shift to lower frequency upon the tensile strain

Summary

Introduction

Thermoelectric materials have drawn considerable attention because they can harvest energy from waste heat by converting thermal energy directly into electrical energy [1,2,3]. The conversion efficiency of a TE material can be evaluated by the dimensionless figure of merit, ZT = S2 σT/(k e + k l ), where S, σ, T are the Seebeck coefficient, the electrical conductivity, and the absolute temperature, respectively. Ke and kl are electronic and lattice thermal conductivities. High thermoelectric performance requires a large thermoelectric power factor (PF =S2 σ) and low thermal conductivity. Recent studies confirmed that the compounds composed of Te and Se have excellent thermoelectric and electronic transport properties [7,8,12]. In our previous work [7], we revealed that the 1T-phase

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Results

Conclusion