Anharmonicity and weak bonding-driven extraordinary thermoelectric performance in wrinkled SnSe monolayer with low lattice thermal conductivity

Abstract

SnSe compound (Nature, 2014, 508, 373–377) has become the star in the field of thermoelectric (TE) materials owing to the environmental friendliness, abundant reserves, and excellent performance. In the present work, the electronic structures, thermal and electronic transport, as well as TE properties of a two-dimensional (2D) wrinkled SnSe monolayer are comprehensively investigated in combination with first-principles calculations and Boltzmann transport theory. The SnSe monolayer is an indirect semiconductor with a bandgap of 2.88 eV using Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional. The “multivalley” band structure of SnSe monolayer is not only beneficial for maximizing the power factor, but also leads to low lattice thermal conductivity (κl) (1.37/1.42 W/mK @ 300 K armchair-/zigzag-direction). The further crystal orbital Hamilton population (COHP) analysis shows that the low κl in SnSe monolayer is attributed to weak antibonding state below the Fermi level, which in turn weakens the chemical bonding and leads to the mutual exclusion of Sn and Se atoms. As a consequence, the softening of phonon modes and a significant reduction in the phonon group velocity are discovered for the SnSe monolayer, which is beneficial for strong anharmonicity and significant phonon scatterings. Additionally, the electronic transport properties of the 2D SnSe monolayer are evaluated by taking into account the electron-phonon interactions, and the optimal ZTs of 2.13 (armchair-direction) and 3.01 (zigzag-direction) are achieved for n-type and p-type SnSe monolayer at 900 K, respectively. Our present work can not only provide fundamental understanding of thermal and electronic transport properties of wrinkled SnSe monolayer, but also shed some light on the theoretical design of low dimensional SnSe-layered material in thermoelectric applications.