Ultralow lattice thermal conductivity and thermoelectric performance of twisted Graphene/Boron Nitride heterostructure through strain engineering

Abstract

We designed and investigated the electronic, mechanical, and thermoelectric properties of Graphene/hexagonal Boron Nitride (Gr/h-BN) heterostructure at various twisting angles based on the Ab-initio simulation. The structural stability was studied at optimized rotation angles (ϕ) = 0∘, 16.10∘, 21.79∘, 38.21∘, 43.90∘ and 60∘. The heterostructure shows semiconducting nature at ϕ=0∘, 21.79∘ and 38.21∘. These twisted heterostructures have demonstrated extraordinary mechanical properties such as Young’s modulus and bulk modulus. Using the semiclassical Boltzmann transport theory, it is observed that the Seebeck coefficient, electric conductivity, and power factor at ϕ=0∘, 21.79∘, 38.21∘, and 60∘ are much higher than the values measured at ϕ=16.10∘ and 43.90∘. Moreover, at ϕ=60∘, the Power Factor for the n-type dopants can reach 1.37 × 1011 W/msK2. The lattice thermal conductivity at room temperature is found to be very low for ϕ=16.10∘, 21.79∘, 43.90∘ and 38.21∘ rotation angles. An ultralow lattice thermal conductivity with a value of 0.095 W/mK at 300K has been observed for 21.79∘ rotation angle, which is lower than other rotation angles because of very low group velocity (22.1 km/s) and short phonon lifetime (∼0.12 ps). The high thermoelectric performance results from an ultralow thermal conductivity arising due to the strong lattice anharmonicity. The present observations can offer significant impact on the design of high performance thermoelectric materials based on twisted van der Waals heterostructure (vdWH).