Theoretical Study On Thermoelectric Performance Of Two-dimensional BAs/WSe₂ Van Der Waals Heterostructure

Industrial production and social life of fossil fuels inevitably emit a lot of waste heat.This waste heat can have some negative effects,for example,the heat buildup can cause the failure of logical computing devices and data storage devices.Thermoelectric technology can directly convert waste heat into useful electricity,which is an effective way to alleviate the above problems.Thermoelectric equipment has the advantages of no moving parts,miniaturization,quiet operation and no emission of greenhouse gases,which is expected to realize a new revolution in energy technology.Usually,the power factor（=²）is used to measure the abilities of the thermoelectric conversion material,dimensionless thermal power optimal value（=²/）is used to estimate the thermoelectric conversion efficiency.It can be seen that thermoelectric materials with high thermoelectric conversion efficiency should have large seebeck coefficient（）,high conductivity（）and low thermal conductivity（）at the same time,is the sum of the lattice thermal conductivity(₇))and the electronic thermal conductivity(₀)).It is difficult to improve the thermoelectric conversion efficiency,the essential reason is that the,andκ_e of materials are mutual coupling,optimize one thermoelectric parameter will affect the others.With the development of thermoelectric materials,carrier energy filtering effect and quantum limiting effect in two-dimensional heterostructure have successfully broken the mutual restriction of thermoelectric parameters.In addition,due to the existence of two-dimensional heterostructure interfaces,phonon scattering can be enhanced to reduce the thermal conductivity of materials.Therefore,the thermoelectric conversion efficiency of two-dimensional heterostructure is often higher than that of two-dimensional monolayer materials,which has great application potential in the field of thermoelectric.Transition metal disulfide compounds（TMDCs）monolayer have become a new platform for exploring two-dimensional semiconductor physics due to their highly controllable band gap,but their inherent thermoelectric properties are far from sufficient for practical applications due to their high lattice thermal conductivity.A large number of interfaces in the in-plane direction of two-dimensional van der Waals（vd W）heterostructure can enhance phonon scattering and reduce lattice thermal conductivity,which is one of the strategies to optimize the thermoelectric performance of TMDCs monolayer.This study selects BAs monolayer with WSe₂ monolayer to form two-dimensional vd W heterostructure as the research object,both are direct band-gap semiconductors and the lattice constants are very close.In this paper,first-principles calculations based on density functional theory and Boltzmann transport theory are used to systematically explore the crystal structure,energy band structure,electric transport parameters,phonon transport parameters and thermoelectric properties of two-dimensional BAs/WSe₂ vd W heterostructure.The results show that the lattice constant is 3.34?,the lattice mismatch ratioδis only 2.39%,and effective thickness is 10.47?.Select the most stable stacking mode from the four highly symmetrical stacking modes to carry out subsequent research,and there is no virtual frequency in phonon dispersion of the two-dimensional BAs/WSe₂ vd W heterostructure,indicating that the structure is dynamically stable.PBE functional is used to calculate the electron band structure of the two-dimensional BAs/WSe₂ vd W heterostructure,and the structure is determined to be a direct bandgap semiconductor.The minima of the conduction band and the maxima of the valence band are at the high symmetry point K with a band gap of 0.65 e V,the band arrangement is of overlapping type.Carrier relaxation time is calculated by using deformation potential theory and electrical transport parameters of the two-dimensional BAs/WSe₂ vd W heterostructure are calculated based on the energy band structure and relaxation time.The calculation results show that theof n-type two-dimensional BAs/WSe₂ vd W heterostructure can reach 208.82 m W m^-1 K^-2 at an optimal carrier concentration at 900 K.Theof n-type two-dimensional BAs/WSe₂ vd W heterostructure shows significant improvement compared with WSe₂ monolayer and BAs monolayer.Then phonon transport parameters of two-dimensional BAs/WSe₂vd W heterostructure are calculated.Lattice thermal conductance₇)decreased significantly with increasing temperature,which is because increasing temperature is conducive to phonon scattering.At 300 K,the₇)of BAs/WSe₂vd W heterostructure is 116.80 W m^-1 k^-1,while the₇)of WSe₂ monolayer and BAs monolayer are 132.12 and 320.18 W m^-1 k^-1,respectively.This is because the formation of heterostructure can provide more complex phonon scattering paths and thus effectively reduce the lattice thermal conductivity of materials.Finally,get the relationship between thevalue of two-dimensional BAs/WSe₂ vd W heterostructure and carrier concentration.At 900 K thevalue of n-type two-dimensional BAs/WSe₂ vd W heterostructure can reach 1.90at an optimal carrier concentration.Significantly improved compared with BAs monolayer and WSe₂ monolayer.Calculation studies in this paper show that two-dimensional BAs/WSe₂ vd W heterostructure are optimized in terms of power factor and lattice thermal conductivity,showing high thermoelectric conversion efficiency and representing a n-type two-dimensional thermoelectric material with great potential.