Designing graphene/hexagonal boron nitride superlattice monolayer with high thermoelectric performance

TL;DR

This paper proposes a graphene/hexagonal boron nitride superlattice monolayer with significantly improved thermoelectric performance, achieving high ZT values through reduced thermal conductivity and optimized electronic properties.

Contribution

It introduces a novel hybrid superlattice design and demonstrates enhanced thermoelectric efficiency using advanced computational methods.

Findings

Lattice thermal conductivity is over 100 times lower than pristine graphene.

Achieves a ZT value of approximately 2.5 at 1100 K for n-type systems.

Carrier transport in the valence band is mainly through graphene, enabling p-type performance enhancement.

Abstract

We design a hybrid graphene/hexagonal boron nitride superlattice monolayer and investigate its thermoelectric properties using density functional theory and Boltzmann transport equations with the relaxation time accurately treated by electron-phonon coupling calculations. Compared with that of pristine graphene, the lattice thermal conductivity of the superlattice structure is more than two orders of magnitude lower due to the enhanced three-phonon scattering process originated from the mixed-bond characteristics. Besides, the coexistence of light and heavy bands around the Fermi level leads to an ultrahigh power factor along the zigzag direction, where the highest ZT value of ~2.5 can be achieved for the n-type system at 1100 K. Moreover, it is noted that the carrier transport near the valance band minimum is almost entirely contributed by the graphene part of the superlattice. As a consequence, the thermoelectric performance of p-type system can be enhanced to be comparable with that of n-type one by appropriate substitution of nitrogen atom with phosphorus, which can suppress the lattice thermal conductivity but nearly have no influence on the hole transport.