Leveraging electron-phonon interaction to enhance the thermoelectric power factor in graphene-like semimetals

Abstract

Electron-phonon interaction (EPI) is presumably detrimental for thermoelectric performance in semiconductors because it limits carrier mobility. Here we show that enhanced EPI with strong energy dependence offers an intrinsic pathway to significant increase in the Seebeck coefficient and the thermoelectric power factor, particularly in the context of two-dimensional (2D) graphene-like Dirac bands. The increase is realized by enabling electron energy filtering through preferential scattering of electron/hole carriers. We prove this concept by implementing state-of-the-art firstprinciples computational methods with explicit treatment of EPI for a 2D gapless MoS2 allotrope, which has both massless Dirac bands and a heavy-fermion state that acts as the filter. We determine that the optimal location of the heavy state and hence the onset of the filtering process is at the Dirac point. Our study opens a new avenue for attaining ultrahigh power factors via engineering the EPI in graphene-like semimetals or identifying new compounds that intrinsically possess the featured electronic structure.

Optimal Band Structure for Thermoelectrics with Realistic Scattering and Bands

“…Using a straightforward but improved approach, we herein fine-tune those blueprints while proposing optimal band structures and design principles along the way. Our generalized findings from this modeling study are mutually supportive of and consistent with the findings from recent targeted studies of high-performing materials with high-fidelity first-principles computations [38,40,54,57,58]. We hope the theoretical investigations of the present study help the community navigate rationally towards next-generation thermoelectrics.…”

“…Detailed results and discussions are provide in supplemental section IIB. It is therefore no surprise that high-performing semimetals and narrow-gap semiconductors feature quite drastic band asymmetries about the Fermi level [38][39][40][41][42][43].…”

Thermoelectrics properties of two-dimensional materials with combination of linear and nonlinear band structures

“…This result is contrary to the mainstream impression that semimetals are generally poor for thermoelectricity [41]. Furthermore, the existence of a heavy parabolic band that intersects Dirac bands at the Fermi level is found to enhance PF due to the improved electron-phonon scattering in the form of a sharp spike of density of states (DOS) [40]. Specifically, the existing heavy band acts as a filter for the low-energy carriers to be excited.…”

“…As we will see later, the existence of a heavy band alongside Dirac bands will improve the thermoelectric performance even with a narrow bandgap. We achieved the maximum value of ZT when the heavy band intersects the Dirac bands at the Fermi level for the parabolic band but not for the other heavy bands [40]. However, removing one linear band will give a better figure of merit ZT for every type of heavy band.…”

“…One can tune the bandgap or change the combination of the band structures to know the optimized structure that will give better TE properties. Several works related to the band engineering have been performed for many types of band structures, such as pudding-mold bands [35][36][37][38][39], parabolic bands [40][41][42], and linear Dirac bands [43]. In particular, the existence of a heavy band alongside the Dirac bands gives a high power factor (PF) in a semimetal like CoSi.…”