Thermoelectric characteristics of X_2YH_2 monolayers (X=Si, Ge; Y=P, As, Sb, Bi): a first-principles study

Mohammad Ali Mohebpour,Sahar Izadi Vishkayi,Shobair Mohammadi Mozvashi,Meysam Bagheri Tagani

doi:10.1038/s41598-021-03280-1

Abstract

Ever since global warming emerged as a serious issue, the development of promising thermoelectric materials has been one of the main hot topics of material science. In this work, we provide an in-depth understanding of the thermoelectric properties of X_2YH_2 monolayers (X=Si, Ge; Y=P, As, Sb, Bi) using the density functional theory combined with the Boltzmann transport equation. The results indicate that the monolayers have very low lattice thermal conductivities in the range of 0.09−0.27 Wm^{-1}K^{-1} at room temperature, which are correlated with the atomic masses of primitive cells. Ge_2PH_2 and Si_2SbH_2 possess the highest mobilities for hole (1894 cm^2V^{-1}s^{-1}) and electron (1629 cm^2V^{-1}s^{-1}), respectively. Si_2BiH_2 shows the largest room-temperature figure of merit, ZT=2.85 in the n-type doping ( sim 3times 10^{12} cm^{-2}), which is predicted to reach 3.49 at 800 K. Additionally, Si_2SbH_2 and Si_2AsH_2 are found to have considerable ZT values above 2 at room temperature. Our findings suggest that the mentioned monolayers are more efficient than the traditional thermoelectric materials such as Bi_2Te_3 and stimulate experimental efforts for novel syntheses and applications.

Highlights

Ever since global warming emerged as a serious issue, the development of promising thermoelectric materials has been one of the main hot topics of material science
Our work introduces a new class of thermoelectric materials which can be synthesized by a conventional process similar to the Sn2BiH2, as their constituent atoms belong to the same family and the former experimental work suggests possibility of similar s yntheses[34]
The structural, dynamical, and thermal stabilities of the monolayers were already validated by cohesive energy, phonon dispersion, and ab-initio molecular dynamics (AIMD) analyses in previous work[33]

Summary

Introduction

Ever since global warming emerged as a serious issue, the development of promising thermoelectric materials has been one of the main hot topics of material science. Thermoelectric (TE) generators are considered as an eco-friendly solution to the global warming issue, since they can convert waste heat into electricity[1,2,3,4,5] They have received considerable attention owing to their scalability, cleanliness, and long operating life[6,7,8]. The conversion efficiency of a TE material is measured by a dimensionless parameter called figure of merit (ZT)[13,14,15] as below: S2σ T. where S, σ , and T are the Seebeck coefficient, electrical conductivity, and absolute temperature, while κe and κL stand for the electronic and lattice thermal conductivities, respectively. A promising TE material must have a large power factor (PF = S2σ ) and low thermal conductivity (κ = κe + κL). It was reported by Liu et al.[28] that Bi0.5 Sb1.5Te3 nanomaterial could have a ZT of ∼1.96 at 420 K, which is higher than those of commercial materials

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Conclusion