Realizing high thermoelectric performance with comparable p- and n-type figure-of-merits in a graphene/h-BN superlattice monolayer.

Carbon-based structures are a superior alternative for unleashing the thermoelectric potential of earth-abundant and environmentally friendly materials. Here we design a hybrid graphene/h-BN superlattice monolayer and investigate its thermoelectric properties based on density functional theory and accurate solution of Boltzmann transport equations. Compared with that of pristine graphene, the lattice thermal conductivity of the superlattice structure is more than two orders of magnitude lower ascribed to the significantly increased phonon scattering originating from the mixed-bond characteristics. Besides, the obvious valley anisotropy near the electronic band edge leads to an ultrahigh power factor along the zigzag direction, which in turn gives an n-type ZT value as high as 2.5 at 1100 K. Moreover, it is interesting to find that the thermoelectric performance of p-type system can be enhanced to be comparable with that of n-type one by appropriate substitution of the nitrogen atom with phosphorus, which can suppress the lattice thermal conductivity but nearly have no effect on the hole transport.

High Thermoelectric Performance Originating from the Grooved Bands in the ZrSe3 Monolayer.

Low-dimensional layered materials have attracted tremendous attentions because of their wide range of physical and chemical properties and potential applications in electronic devices. Using first-principles method taking into account the quasi-particle self-energy correction and Boltzmann transport theory, the electronic transport properties of the ZrSe3 monolayer are investigated, where the carrier relaxation time is accurately calculated within the framework of electron-phonon coupling. It is demonstrated that the high power factor of the monolayer can be attributed to the grooved bands near the conduction band minimum. Combined with the low lattice thermal conductivity obtained by solving the phonon Boltzmann transport equation, a considerable n-type ZT value of ∼2.4 can be achieved at 800 K in the ZrSe3 monolayer.

Large-scale calculations of thermoelectric transport coefficients: a case study of γ-graphyne with point defects.

Defects such as vacancies and impurities could have profound effects on the transport properties of thermoelectric materials. However, it is usually quite difficult to directly calculate the thermoelectric properties of defect-containing systems via first-principles methods since a very large supercell is required. In this work, based on the linear response theory and the kernel polynomial method, we present an efficient approach that can help to calculate the thermoelectric transport coefficients of a large system containing millions of atoms at arbitrary chemical potential and temperature. As a prototype example, we consider dilute vacancies and hydrogen impurities in a large-scale γ-graphyne sheet and discuss their effects on the thermoelectric transport properties.