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| Paper IPM / P / 17148 |
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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$_2$YH$_2$ 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$_2$PH$_2$ and Si$_2$SbH$_2$ possess the highest mobilities for hole (1894 cm$^2$V$^{-1}$s$^{-1}$) and electron (1629 cm$^2$V$^{-1}$s$^{-1}$ ),
respectively. Si$_2$BiH$_2$ shows the largest room-temperature figure of merit, ZT = 2.85 in the n-type doping ($\sim$ 3 $\times$ 10$^{12}$ cm$^{-2}$ ), which is predicted to reach 3.49 at 800 K. Additionally, Si$_2$SbH$_2$ and Si$_2$AsH$_2$ 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$_2$Te$_3$
and stimulate experimental efforts for novel syntheses and applications.
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