The first-principles study on phononic thermal transport properties in two-dimensional materials and its applications in thermoelectric and thermal management

Abstract

The lattice thermal conductivity is an intrinsic and essential transport property that plays an important role in thermoelectric devices and thermal management of electronics. We use density functional theory (DFT) combined phonon Boltzmann transport equation (PBTE) to predict the lattice thermal conductivity of two-dimensional materials. The second and third order derivatives of the energy with respect to the atomic position are the most important ingredients in the calculation of lattice thermal conductivity, and we obtain these derivatives from DFT through finite differences method. The approach is applied to compute phononic thermal transport in the variety of two-dimensional material. We studied the electronic structures, Seebeck coefficients, electrical conductivities, lattice thermal conductivities, and figures of merit of two-dimensional IV-VI compounds, which showed that the thermoelectric performance of these two-dimensional compounds is improved in comparison to their bulk phases. High figures of merit (ZT ) are predicted for SnSe (ZT = 2.63, 2.46), SnS (ZT = 1.75, 1.88), GeSe (ZT = 1.99, 1.73), and GeS (ZT = 1.85, 1.29) at 700 K along armchair and zigzag directions, respectively. We also calculate the lattice thermal conductivity of the monolayer SnX2 and monolayer InX and It is found that the lattice thermal conductivity of these monolayers at room temperature is very low, which is attributed to the heavy atomic masses of Sn, In, S, Se, and Te and its strong phonon anharmonicity. The strain is a handy and useful tool to enhance the performance of the semiconducting devices. We find that the lattice thermal conductivity is reduced approximately 2.5 times at 8% tensile strain for the two-dimensional 2H-MoTe2 contrary to graphene, germanene, silicene, germanene, and Penta-SiC2. The reduction in lattice thermal conductivity attributes to the reduction in the phonon group velocity, the phonon heat capacity, and the phonon scattering time. Heat removal has become a significant challenge in the miniaturization of electronic devices, especially in power electronics, so semiconducting materials with suitable bandgap and high lattice thermal conductivity are highly desired. Here, we theoretical predict an ultra-high and anisotropic lattice thermal conductivity in the monolayer BC2N. The predicted values of lattice thermal conductivity at room-temperature are 893.90 W/mK and 1275.79 W/mK along armchair and zigzag directions, respectively. These values are probably the highest that have ever been reported for the two-dimensional semiconducting materials.