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.
Green's functions of the Boltzmann transport equation with the full scattering matrix for phonon nanoscale transport beyond the relaxation-time approximation