Monolayer Ag₂S: Ultralow Lattice Thermal Conductivity and Excellent Thermoelectric Performance

Abstract

For efficient thermoelectric materials, high power factor and low lattice thermal conductivity are desired properties. Therefore, the high lattice thermal conductivity of twodimensional materials limits their usage in thermoelectric applications. We employ firstprinciples calculations along with semiclassical Boltzmann transport theory for the electron and phonon dynamics to investigate the thermoelectric properties of nonmetal-shrouded monolayer Ag 2 S. We show that the simultaneous presence of flat and dispersive bands in the vicinity of the conduction band edge leads to a high power factor, while close proximity of the acoustic and optical bands in the phonon dispersion results in low thermal conductivity. With moderate electron doping, a high in-plane thermoelectric figure of merit is achieved. Our results demonstrate great potential of nonmetal-shrouded monolayer Ag 2 S in thermoelectric applications.

Extraordinary lattice thermal conductivity of gold sulfide monolayers

“…Based on our results, phonons with extremely low MFP of about 0.1 nm contribute to the lattice thermal conductivity of β-Au 2 S, while in other gold sulfide monolayers the lowest phonon MFP that contribute to κ is about 1.0 nm. Contribution from phonons with such low phonon MFP is previously seen in Ag 2 S, which also has an ultralow κ , 35 and is characteristic of low thermal conductivity amorphous structures. 43 However, as such low phonon MFPs are comparable or even smaller than the unit cell size of these systems, the definition of phonons with such low MFPs can be questionable.…”

“…Very interestingly, as opposed to what is typically found, the optical modes are the dominant heat carriers in gold sulfide monolayers. High optical mode contribution to heat transport has also previously observed in monolayer Ag 2 S. 35 This feature can be attributed to the complex structure of gold sulfide monolayers and the overlap of low frequency optical phonons with the LA mode (see Fig. 2 ).…”

“…First we consider the phonon scattering rates of monolayer Ag 2 S presented in ref. 35 . In the frequency region that contributes to κ , most of the acoustic and optical phonons have scattering rates lower than 10 ps −1 , which corresponds to a lifetime longer than 0.1 ps.…”

Lattice Instability and Ultralow Lattice Thermal Conductivity of Layered PbIF

“…The discovery and design of materials with ultralow lattice thermal conductivity (κ l ) receive tremendous research interest because of potential applications in energy conversion technology. Additionally, (ultra)­low κ l materials with wide band gaps have promising applications in thermal barrier coatings. , Ultralow κ l materials with narrow band gaps are suitable for thermoelectric applications. − Several strategies , have been proposed to design ultralow κ l materials including resonant bonding, rattling, − cation disorder, bonding heterogeneity, − and lone pair induced anharmonicity. − Combining two or more of these in one material suppresses κ l effectively. For instance, a lone pair enhances the anharmonicity, while bonding heterogeneity results in anisotropic κ l with poor phonon transport along the weak bonding (soft) lattice direction.…”

Geometry and Greatly Enhanced Thermoelectric Performance of Monolayer MXY Transition‐Metal Dichalcogenide: MoSTe as an Example

“…2D materials have been widely studied in thermoelectric research and applications. [17][18][19][20][21][22] In addition to the limited dimensions and reduced size, the lattice thermal conductivity can also be reduced by phonon-engineering with almost unchanged electron transport. [23][24][25][26][27][28] In general, many efforts have been made to improve the thermoelectric performance.…”