Thermoelectric characteristics of X$$_2$$YH$$_2$$ monolayers (X=Si, Ge; Y=P, As, Sb, Bi): a first-principles study

Abstract

AbstractEver 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$$_2$$ 2 YH$$_2$$ 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$$^{-1}$$ - 1 K$$^{-1}$$ - 1 at room temperature, which are correlated with the atomic masses of primitive cells. Ge$$_2$$ 2 PH$$_2$$ 2 and Si$$_2$$ 2 SbH$$_2$$ 2 possess the highest mobilities for hole (1894 cm$$^2$$ 2 V$$^{-1}$$ - 1 s$$^{-1}$$ - 1 ) and electron (1629 cm$$^2$$ 2 V$$^{-1}$$ - 1 s$$^{-1}$$ - 1 ), respectively. Si$$_2$$ 2 BiH$$_2$$ 2 shows the largest room-temperature figure of merit, $$ZT=2.85$$ Z T = 2.85 in the n-type doping ( $$\sim 3\times 10^{12}$$ ∼ 3 × 10 12  cm$$^{-2}$$ - 2 ), which is predicted to reach 3.49 at 800 K. Additionally, Si$$_2$$ 2 SbH$$_2$$ 2 and Si$$_2$$ 2 AsH$$_2$$ 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$$_2$$ 2 Te$$_3$$ 3 and stimulate experimental efforts for novel syntheses and applications.