Materials selection rules for optimum power factor in two-dimensional thermoelectrics

Abstract

Two-dimensional (2D) materials have emerged as the ideal candidates for many applications, including nanoelectronics, low-power devices, and sensors. Several 2D materials have been shown to possess large Seebeck coefficients, thus making them suitable for thermoelectric (TE) energy conversion. Whether even higher TE power factors can be discovered among the ≈2000 possible 2D materials (Mounet et al 2018 Nat. Nanotechnol. 13 246-52) is an open question. This study aims at formulating selection rules to guide the search for superior 2D TE materials without the need for expensive atomistic simulations. We show that a 2D material having a combination of low effective mass, higher separation in the height of the step-like density of states, and valley splitting, which is the energy difference between the bottom of conduction band and the satellite valley, equal to 5 k B T will lead to a higher TE power factor. Further, we find that inelastic scattering with optical phonons plays a significant role: if inelastic scattering is the dominant mechanism and the energy of the optical phonon equals 5 k B T, then the TE power factor is maximized. Starting from a model for carrier transport in MoS 2 and progressively introducing the aforementioned features results in a two-orders-ofmagnitude improvement in the power factor. Compared to the existing selection rules or material descriptors, features identified in this study provide the ability to comprehensively evaluate TE capability of a material and helps in identifying future TE materials suitable for applications in wasteheat scavenging, thermal sensors, and nanoelectronics cooling.

Low Thermal Conductivity and High Thermoelectric Performance of Kagome‐Like As and Sb Monolayers: A First‐Principles Study

“…This type of band structure can lead to a large Seebeck coefficient and high electrical conductivity, which favors high TE performance. [ 15 ]…”

General strategies to improve thermoelectric performance with an emphasis on tin and germanium chalcogenides as thermoelectric materials

“…A simple model based on effective mass approximation predicts that inelastic scattering in 2D semiconducting materials with step-like DOS can ensure a high power factor. 190 The inelastic processes delay the onset of scattering and maximize the utilization of the Fermi window for transport. The simulations showed that the materials with dominant inelastic processes, specifically when optical phonon energy E ph ∼ 5 k B T , improve the power factor.…”

Very high thermoelectric power factor near magic angle in twisted bilayer graphene

“…This combination of features in the DOS, in addition to the secondary bandgap between the lowest and second subbands in TBG, creates a narrow transport distribution function (TDF) [16]. Then states bunched around sharp features in the DOS translate into improved Seebeck coefficient and maximize the PF [17,18]. The highly tunable band structure of TBG offers a new lever of control and a novel avenue to further decouple Seebeck and conductivity to achieve unprecedented PFs.…”