Phonon Coupled Scattering Caused Ultralow Lattice Thermal Conductivity and Its Role in The Remarkable Thermoelectric Performance of Newly Predicted SiS2 and SiSe2 monolayers

TL;DR

This study predicts that SiS2 and SiSe2 monolayers exhibit ultralow lattice thermal conductivity due to phonon-phonon coupling, leading to high thermoelectric efficiency, making them promising for power generation.

Contribution

It introduces newly predicted 2D SiS2 and SiSe2 monolayers with ultralow thermal conductivity and high thermoelectric performance based on DFT and Boltzmann transport calculations.

Findings

Lattice thermal conductivity (kph) is ultralow in SiS2 and SiSe2 monolayers.

High thermoelectric figure of merit (ZT) of 0.78 and 0.80 at 500K.

p-type doping enhances thermoelectric performance.

Abstract

For high efficiency thermoelectric power conversion not only improvement of materials properties but also prediction and synthesis of new thermoelectric materials is needed. Here we have carried out a systematic investigation on thermoelectric performance of newly predicted two dimensional (2D) semiconducting SiS2 and SiSe2 monolayers of group IVA-VIA family using density functional theory (DFT) and Boltzmann transport equation (BTE). Our computed values of lattice thermal conductivity (kph) are ultralow which result very high thermoelectric figure of merit (ZT) value of 0.78 (0.80) at 500K in SiS2 (SiSe2) monolayer. The ultralow values of kph are attributed to phonon-phonon coupling of acoustic and low frequency optical branches which leads to larger scattering, low group velocity, smaller mean free path and shorter lifetime of phonons. It is also found from our investigation that p-type doping is more effective than n-type doping to get optimal power factor (PF) and ZT. Our theoretical investigation suggests that newly predicted semiconducting SiS2 and SiSe2 monolayers can be very promising thermoelectric materials for fabrication of high efficiency thermoelectric power generator to convert wastage heat into electricity.