First-principles Study Of Multi-Level Doping In ?-? Thermoelectric Materials

Thermoelectric materials can realize the mutual conversion of electrical energy and thermal energy.The biggest feature is that they can use the temperature difference in nature to provide thermoelectric power generation for human beings,so they can greatly improve the efficiency of energy utilization,and there is no problem of environmental pollution,and it has a good integration.Social benefits and good application prospects in the field of new energy materials.Thermoelectric figure of merit is an important physical parameter that characterizes thermoelectric conversion efficiency.The development of high-performance thermoelectric materials is of great significance to scientific research and practical applications.The main purpose of this paper is to predict the method of improving the thermoelectric performance of IV-VI thermoelectric materials through first-principles calculations.In this paper,by adopting a first-principles calculation method based on density functional theory,by studying the electronic structure changes of PbTe,PbSe,Pb S,GeTe,and SnTe doped with group III elements,it has been screened out that it can be introduced the resonance energy level and deep energy level impuritys in each system.and the improvement effect of resonance energy level on the thermoelectric performance of each system is quantified through Boltzmann electric transport calculation.For the PbTe system,the doping of Ga and Tl can form a resonance energy level in the valence band.The introduction of Ga can increase the electrical performance of the PbTe system by about 50%,and the introduction of Tl can increase the electrical performance of the PbTe system by about 100%.Doping In to PbTe can form a deep energy level in a semi-full state.On the basis of PbTe doping In,it is proposed to use halogen elements Cl,Br,and I as shallow energy level impurities.Both can provide a large number of electrons for PbTe,are n-type doped,and can optimize the carrier concentration in a wide temperature range.Doping Al in both PbSe and Pb S systems can form resonance energy levels in the conduction band.Al can increase the electrical properties of PbSe by about100%and the electrical properties of Pb S by about 70%.Doping Ga and In into the GeTe system can form resonance energy levels in the valence band,and doping Bi and Sb can reduce the concentration of intrinsic vacancy defects,increase the Seebeck coefficient,and reduce the thermal conductivity.The use of Ga-Bi,Ga-Sb,In-Bi,and In-Sb co-doping in GeTe can further improve the thermoelectric performance.These four doping methods not only expand the band gap but also promote the convergence of the valence band,so it can increase the energy with degeneracy,the Seebeck coefficient is further improved.The calculation found that since In-Bi and In-Sb are more capable of promoting energy band degeneration than Ga-Bi and Ga-Sb,the effect of In is better than Ga for double doping.For the SnTe system,incorporation of In can form a resonance energy level in the valence band,and the introduction of Al element can form a semi-filled deep energy level.Because SnTe also has a large number of Sn vacancies,the intrinsic carrier concentration of the system is too high,?10²¹ cm^-3 order of magnitude,and the deep level can confine some carriers,so it is predicted that single doping of In or Al in SnTe can improve the thermoelectric performance of SnTe.