Thermoelectric Figure of Merit of a Superatomic Crystal Re6Se8I2 Monolayer

Abstract

Superatomic materials are newly emerging candidates for high-performance thermoelectric (TE) devices due to their intrinsic ultralow thermal conductivities. However, the low TE power factor becomes a huge obstacle to reaching the required dimensionless figure of merit (ZT) values for practical applications. Here, motivated by the recently synthesized superatomic ${\mathrm{Re}}_{6}{\mathrm{Se}}_{8}{\mathrm{I}}_{2}$ monolayer [He et al. J. Am. Chem. Soc. 144, 74 (2022)], we study its superior TE properties by using density functional theory combined with phonon Boltzmann transport theory and deep potential molecular dynamics. We show that the large mass and anharmonic $\mathrm{Re}---\mathrm{I}$ bonds introduce strong phonon scattering and result in a low lattice thermal conductivity of 1.20 W m${}^{\ensuremath{-}1}$ K${}^{\ensuremath{-}1}$ at 300 K, while the strong and harmonic $\mathrm{Re}---\mathrm{Se}$ network ensures a high TE power factor of 4344 \textmu{}W m${}^{\ensuremath{-}1}$ K${}^{\ensuremath{-}2}$ in the b direction for n-type doping. This is an order of magnitude higher than those of other cluster-based materials. Owing to the low thermal conductivity and high TE power factor, ${\mathrm{Re}}_{6}{\mathrm{Se}}_{8}{\mathrm{I}}_{2}$ exhibits higher ZT values of 1.20 (500 K) and 1.43 (900 K) with n-type doping along the b direction compared with other cluster-based TE materials reported so far.