Thermoelectric Properties Of Se Doped Sb₂Te₃ Nanofilms

Thermoelectric material is a new kind of functional material which realizes the direct conversion of heat and electric energy through the movement of carrier(electron or hole)in solid.Sb₂Te₃ based compound and its solid solution alloy are one of the most mature thermoelectric materials.At present,most thermoelectric refrigeration components are made of this kind of material,which is recognized as the best low temperature thermoelectric material.But its thermoelectric efficiency is still limited.Through low dimensional treatment and reasonable doping,the introduction of appropriate short-range disorder into the crystal structure of the material can reduce the thermal conductivity,and at the same time,along with a certain change of band gap width,optimize the carrier concentration,which can effectively improve the thermoelectric properties of the material.In this paper,the thermoelectric properties of two-dimensional monolayer Sb₂Te₂Se are theoretically simulated by using the combination of first principles and Boltzmann transport theory.Firstly,the electronic band structure of the material is studied,and then the electron transport and phonon transport are theoretically analyzed.Finally,the thermoelectric optimal value of the material is obtained.The band gap of monolayer Sb₂Te₂Se is indirect,and the size of band gap is moderate,0.95 e V.The Seebeck coefficient of p-type doped monolayer Sb₂Te₂Se is slightly higher than that of n-type monolayer because the valence band density at Fermi surface is slightly higher than that of conduction band and the valence band is degenerate.The Seebeck coefficient is highest at 300K.Seebeck's coefficient increases with the increase of effective energy band mass m_b^*,while the change of electrical conductivity is opposite.However,the relaxation time of the hole is smaller than that of the electron.Under the influence of the relaxation time,the p-type?/?is higher than that of the n-type at the high chemical potential.The difference between p-type?/?and n-type?/?is not significant at low chemical potentials.No matter p-type or n-type,there is little difference in conductivity at different temperatures under the same mobility.The strong coupling of the acousto-optic modes enhances phonon scattering and leads to low lattice thermal conductivity.The low lattice thermal conductivity of monolayer Sb₂Te₂Se is mainly caused by the coupling of heavy elements and acoustooptic branching.The optimum Z_eT value of monolayer Sb₂Te₂Se is very high because of the low lattice thermal conductivity.For better n-type,the Z_eT reaches 1.5 at1000K,indicating that monolayer Sb₂Te₂Se is a good choice of thermoelectric material.The electronic structure and thermoelectric properties of the two-dimensional monolayer Sb₂Te_3-xSe_x(x=1/6,1/12,1/18,1/27,1/36 and 1/48)were also simulated by using the combination of first principles and Boltzmann transport theory.The electronic band structure of materials and the effect of doping amount on thermoelectric properties were studied.The coupling of the contributions of atoms to the density of states in the monolayer Sb₂Te_3-xSe_x(x=1/6,1/12,1/18,1/27,1/36,and 1/48)mainly affects the Seebeck coefficient,but has little effect on the conductivity.The band gap has a large effect on the electrical conductivity and thus the thermal conductivity of the electron.The effect of temperature on the monolayer Sb₂Te_3-xSe_x is different with the difference of x.When x=1/36,the temperature increases and the Z_eT decreases.When x=1/12,p-type monolayer Sb₂Te_3-1/12Se_1/12 decreases with increasing temperature.N-type monolayer Sb₂Te_3-1/12Se_1/12 increases with increasing temperature.When x=1/12 and x=1/36,the monolayer Sb₂Te_3-xSe_x has the best thermoelectric performance.When x=1/6 and x=1/27,the thermoelectric performance of monolayer Sb₂Te_3-xSe_x is the worst.Therefore,it is not the case that the smaller or greater the doping amount of x,the better the thermal and electrical properties of monolayer Sb₂Te_3-xSe_x are.