Significantly reduced thermal conductivity and enhanced thermoelectric performance of twisted bilayer graphene

Abstract

Twisted bilayer graphene (tBLG) is an intriguing low-dimensional material due to the possible modulation of electronic and thermal properties and a subject of intense research, both for its fundamental physics as well as for its potential in technological applications. Here, the thermoelectric properties of bilayer graphene are investigated for twist angles of 0° and 20°. The thermoelectric properties are calculated using density functional theory, molecular dynamics, and Boltzmann transport theory. An increase in the power factor is observed for 20° tBLG due to an increase in the Seebeck coefficient by 2.2 times at 700 K. The thermal conductivity for 20° tBLG is reduced by 20% and 22% for 325 and 700 K, respectively, as compared to BLG. Consequently, an overall ∼3 times enhancement of a thermoelectric figure of merit (ZT) for 20° tBLG compared to BLG at 700 K is obtained. A strong effect of boundary scattering on thermal transport is observed. However, for electron transport, it is negligible for 20° tBLG. Due to this combined effect, an increase of 194 times in ZT is obtained at a ribbon width of L=10 nm and T = 700 K for 20° tBLG. This indicates that 20° twisted bilayer graphene could be an efficient thermoelectric power generator and can be a suitable material for carbon-based technology and devices.