Quantum transport simulations for the thermoelectric power factor in 2D nanocomposites

Some of the most promising candidates for next-generation thermoelectrics are nanocomposites due to their low thermal conductivities that result from phonon scattering on the boundaries of the various material phases. However, in order to maximize the figure of merit ZT, it is important to understand the impact of such features on the thermoelectric power factor. In this work we consider the effect that nanoinclusions and voids have on the electronic and thermoelectric coefficients of two-dimensional geometries using the fully quantum mechanical Non-Equilibrium Green's Function method. This method combines in a unified approach the details of geometry, electron-phonon interactions, quantisation, tunnelling, and the ballistic to diffusive nature of transport. We show that as long as the barrier height is low nanoinclusions can have a positive impact on the Seebeck coefficient and the power factor is not severely impacted by a reduction in conductance. The power factor is also shown to be approximately independent of nanoinclusion and void density in the ballistic case. On the other hand, in the presence of phonon scattering voids degrade the power factor and their influence increases with density. (C) 2019 Elsevier Ltd. All rights reserved.