First-principles Study On Thermoelectric And Optoelectric Properties Of The ?A Group Compounds

Binary compounds of the sixth main group,especially binary tellurides,have excellent optoelectric properties and thermoelectric properties,and are promising candidate materials in the fields of semiconductor devices,solar cells,and thermoelectric generators.1.In this paper,we use the first principles based on density functional theory to theoretically study the stability,electronic structure,thermoelectric properties and photoelectric properties of the material Ba2X6(X=Te,Se,S).The phonon spectrum has no negative frequency in the entire Brillouin zone,indicating that the material has thermodynamic stability.The first-principles calculation results of electronic properties indicate that the material Ba2X6(X=Te,Se,S)is an indirect band gap semiconductor and has a covalent bond between X-X.The calculation results of a series of related parameters of its photoelectric characteristics show that the material has good absorption capacity in the visible region.In addition,it can be found from the energy band diagram that p-type Ba2X6(X=Te,Se,S)is more suitable for thermoelectric materials than n-type.By combining the first principles of Boltzmann theory,the thermoelectric properties of p-type Ba2X6(X=Te,Se,S)at 300-800 K were explored.2.By combining the first-principles particle swarm optimization algorithm for structural prediction software package Calypso,we obtained the new structure Tl4Te6.The calculation results of the phonon spectrum prove that the material is thermodynamically stable,and we further calculated its electronic structure,optoelectric properties and thermoelectric properties.The calculation result of the energy band structure shows that the material is an indirect semiconductor and the band gaps are 0.724eV(PBE functional)and 1.091eV(HSE06 functional).Through the analysis of the local charge density digram,it is found that3.the material has both ionic and covalent bonds.It can be known from the absorption coefficient graph and dielectric imaginary part graph of Tl4Te6 material that the material has good absorption capacity in the visible to far ultraviolet region.In addition,according to the research results of thermoelectric properties,the p-type Tl4Te6 has good thermoelectric properties at 800K,and its maximum ZT can reach 2.47.