A giant thermoelectric figure of merit and ultra-low lattice thermal conductivity using Janus Ge2SeTe monolayer: a first principle investigation

Janus materials exhibit novel and interesting characteristics with a diversified potential applications. These owe to their unique property of structural asymmetry, which break the out-of-plane reflection and lead to a spontaneous electric field. This manuscript investigates a group-IV dichalcogenide Janus monolayer G e 2 S e T e in detail for its thermoelectric performance. The density functional theory has been used as a toolkit for this investigation. The absence of imaginary frequency in the phonon spectra confirms the dynamic stability of the investigated structure. Moreover, to confirm the thermal stability of the system, we have performed the AIMD (Ab-Initio Molecular Dynamics) calculation using the Car-Parllinno algorithm which assures that the structure, is thermally stable. The elastic constants have also been calculated to keep track of mechanical stability. To achieve high accuracy and precise calculations, we have used Hybrid functional (HSE06) to model the exchange-correlation, and deformation potential approach to estimate the scattering time ( τ ). All the thermoelectric transport parameters were calculated by solving the Boltzmann transport equation with a constant relaxation time approximation. The research findings reveal that the investigated monolayer exhibit an ultra-low lattice thermal conductivity of the order of 0.13 W m - 1 K - 1 at room temperature and 0.04 W m - 1 K - 1 at 900 K with outstanding thermoelectric figure of merit (nearly 2.12 at room temperature and 3.52 at 550 K). The superlative thermoelectric performance of Janus monolayer G e 2 S e T e makes it suitable for an efficient thermoelectric device at mid-temperature regimes.