# Potential 2D thermoelectric materials ATeI (A=Sb and Bi) monolayers from a first-principles study

## TL;DR

This study uses first-principles calculations to explore the thermoelectric properties of SbTeI and BiTeI monolayers, revealing their low thermal conductance and promising thermoelectric efficiency, especially under p-type doping.

## Contribution

It provides a systematic theoretical investigation of ATeI monolayers' thermoelectric properties, highlighting their potential as efficient 2D thermoelectric materials.

## Key findings

- Low sheet thermal conductance compared to other 2D materials.
- High thermoelectric figure of merit (ZT) at room temperature.
- P-type doping yields better thermoelectric performance.

## Abstract

Lots of two-dimensional (2D) materials have been predicted theoretically, and further confirmed in experiment, which have wide applications in nanoscale electronic, optoelectronic and thermoelectric devices. Here, the thermoelectric properties of ATeI (A=Sb and Bi) monolayers are systematically investigated, based on semiclassical Boltzmann transport theory. It is found that spin-orbit coupling (SOC) has important effects on electronic transport coefficients in p-type doping, but neglectful influences on n-type ones. The room-temperature sheet thermal conductance is 14.2 $\mathrm{W K^{-1}}$ for SbTeI and 12.6 $\mathrm{W K^{-1}}$ for BiTeI, which are lower than one of most well-known 2D materials, such as transition-metal dichalcogenide, group IV-VI, group-VA and group-IV monolayers. By analyzing group velocities and phonon lifetimes, the very low sheet thermal conductance of ATeI (A=Sb and Bi) monolayers is mainly due to small group velocities. It is found that the high-frequency optical branches contribute significantly to the total thermal conductivity, being obviously different from usual picture with little contribution from optical branches. According to cumulative lattice thermal conductivity with respect to phonon mean free path (MFP), it is difficulty to further reduce lattice thermal conductivity by nanostructures. Finally, possible thermoelectric figure of merit $ZT$ of ATeI (A=Sb and Bi) monolayers are calculated. It is found that the p-type doping has more excellent thermoelectric properties than n-type doping, and at room temperature, the peak $ZT$ can reach 1.11 for SbTeI and 0.87 for BiTeI, respectively. These results make us believe that ATeI (A=Sb and Bi) monolayers may be potential 2D thermoelectric materials, and can stimulate further experimental works to synthesize these monolayers.