Issue 31, 2016

First principles calculations of solid-state thermionic transport in layered van der Waals heterostructures

Abstract

This work aims at understanding solid-state energy conversion and transport in layered (van der Waals) heterostructures in contact with metallic electrodes via a first-principles approach. As an illustration, a graphene/phosphorene/graphene heterostructure in contact with gold electrodes is studied by using density functional theory (DFT)-based first principles calculations combined with real space Green's function (GF) formalism. We show that for a monolayer phosphorene, quantum tunneling dominates the transport. By adding more phosphorene layers, one can switch from tunneling-dominated transport to thermionic-dominated transport, resulting in transporting more heat per charge carrier, thus, enhancing the cooling coefficient of performance. The use of layered van der Waals heterostructures has two advantages: (a) thermionic transport barriers can be tuned by changing the number of layers, and (b) thermal conductance across these non-covalent structures is very weak. The phonon thermal conductance of the present van der Waals heterostructure is found to be 4.1 MW m−2 K−1 which is one order of magnitude lower than the lowest value for that of covalently-bonded interfaces. The thermionic coefficient of performance for the proposed device is 18.5 at 600 K corresponding to an equivalent ZT of 0.13, which is significant for nanoscale devices. This study shows that layered van der Waals structures have great potential to be used as solid-state energy-conversion devices.

Graphical abstract: First principles calculations of solid-state thermionic transport in layered van der Waals heterostructures

Supplementary files

Article information

Article type
Communication
Submitted
23 Mar 2016
Accepted
05 Jun 2016
First published
06 Jun 2016

Nanoscale, 2016,8, 14695-14704

First principles calculations of solid-state thermionic transport in layered van der Waals heterostructures

X. Wang, M. Zebarjadi and K. Esfarjani, Nanoscale, 2016, 8, 14695 DOI: 10.1039/C6NR02436J

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