Thermoelectric characteristics of X $$_2$$ 2 YH $$_2$$ 2 monolayers (X=Si, Ge; Y=P, As, Sb, Bi): a first-principles study

Abstract

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 $$_2$$ 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.