Two-dimensional BiSbTeX2 (X = S, Se, Te) and their Janus monolayers as efficient thermoelectric materials†

Abstract

Today, there is a huge need for highly efficient and sustainable energy resources to tackle environmental degradation and energy crisis. We have analyzed the electronic, mechanical and thermoelectric (TE) characteristics of two-dimensional (2D) BiSbTeX₂ (X = S, Se and Te) and Janus BiSbTeXY (X/Y = S, Se and Te) monolayers by implementing first principles simulations. These monolayers' dynamic stability and thermal stability have been demonstrated through phonon dispersion spectra and ab initio molecular dynamics (AIMD) simulations, respectively. The band structure of these monolayers can be tuned by applying uniaxial and biaxial strains. The investigated lattice thermal conductivity (κ_l) for these monolayers lies between 0.23 and 0.37 W m⁻¹ K⁻¹ at 300 K. For a more precise calculation of the scattering rate, we implemented electron–phonon coupling (EPC) and spin–orbit coupling effects to calculate the transport properties. For p(n)-type carriers, the power factor of these monolayers is predicted to be as high as 2.08 × 10⁻³ W m⁻¹ K⁻² and (0.47 × 10⁻³ W m⁻¹ K⁻²) at 300 K. The higher thermoelectric figure of merit (ZT) of p-type carriers at 300 K is obtained because of their very low value of κ_l and high power factor. Our theoretical investigation predicts that these monolayers can be potential candidates for fabricating highly efficient thermoelectric power generators.