Optimization Of Thermoelectric Properties Of Higher Manganese Silicide And InSb And Construction Of Photothermal Coupling Device

With the rapid development of the global economy,the issues of energy shortage and environmental pollution have become increasingly prominent.As an environmentally friendly energy conversion material,thermoelectric materials have attracted increasing attention.Currently,most commercial thermoelectric materials contain toxic or rare elements,which is not conducive to the large-scale application of thermoelectric technology.In this thesis,green higher manganese silicide（HMS）and InSb semiconductors are taken as the research objects,and some strategies such as element doping,nanocomposite and defect engineering are explored to optimize the thermoelectric performance.This provides guidance for the development of new thermoelectric materials.Based on this foundation,an InSb-based photothermal coupling device was designed and constructed to study its characteristics in solar thermoelectric power generation（STEG）characteristics were studied.The main research contents and conclusions are as follows:1.The thermoelectric properties of HMS were improved by anion S doping and cation Ag doping.The density of crystal defects（dislocations,point defects,Mn S nano-inclusions,nanopores and grain boundaries）are increased significantly by the introduction of S,reducing the lattice thermal conductivity effectively.The peak z T value of（HMS）_0.99（Mn S）_0.01 sample is0.59 at 823 K.The S-doped HMS sample shows an excellent performance/price ratio,which demonstrates it is a potential medium-temperature thermoelectric material.The carrier concentration is increased due to the difference of the valence state of the element after Ag doping.At the same time,Ag doping can introduce point defects,enhancing high-frequency phonon scattering,and reducing the lattice thermal conductivity effectively.The peak z T value of Mn_0.99Ag_0.01Si_1.8 sample is 0.57 at 823 K.2.Element doping and nanocomposite effects were successfully achieved by introducing Ag/Pt alloy quantum dots and CsPbBr₃ perovskite quantum dots into the HMS matrix.Acceptor doping effect can be achieved by Ag doping and Cs doping,increasing the carrier concentration.Meanwhile,Seebeck coefficients can be improved by the energy filtering effect owing to the existence of nano-inclusion phase.On the other hand,phonon scattering is enhanced,reducing the lattice thermal conductivity.The optimal z T values are 0.64 and 0.57 at 823 K,respectively in this study.This strategy provides a new idea for synergistically regulating the electrical and thermal properties of HMS-based materials.3.The thermoelectric performance of N-type InSb are effectively enhanced by doping,constructing porous structure and nano-composite strategy.The carrier concentration can be improved by Sn doping（improving the conductivities）.Meanwhile,the effective mass is improved by the introduced resonance level,which is attributed to the contribution of the 5s and 5p orbitals of Sn,resulting in an increase in the Seebeck coefficients.Finally,the z T peak of the Sn_0.00125InSb sample reaches 0.80 at 723 K.The mobility of InSb is effectively improved by compounding a small amount of Bi I₃.A large number of nano-scale holes and high-density dislocations are introduced after annealing treatment,reducing the lattice thermal conductivity.The optimal z T value reaches 0.89（723 K）.The incorporation of Ag/Pt nanoparticles into the InSb matrix not only significantly reduces the lattice thermal conductivity,but also achieves element doping and energy filtering effects,which synergistically optimizes the electrical and acoustic transport properties of the InSb.Finally,The z T value reaches 0.81 at 703 K.These strategies can effectively optimize the thermoelectric properties of N-type InSb and provide guidance for the subsequent research of InSb-based thermoelectric materials.4.The N-P type transition of InSb is realized by Cd doping.The P-N transition in the range of 323 K–723 K is achieved in the In_1-xCd_xSb samples（x≤0.001）prepared by vacuum melting method,which is mainly due to that the mobility of electron is much higher than that of hole.The In_1-xCd_xSb（x=0.0025–0.1）samples exhibit P-type semiconductor properties over the entire test temperature range.The power factor reaches 1.91×10^-3 W m^-1K^-2 at 723 K due to the increase of conductivity and the decrease of bipolar diffusion effect caused by the high carrier concentration.In addition,the lattice thermal conductivity is decreased to 2.0 W m^-1 K^-1at 723 K due to the enhancement of phonon scattering and the weakening of bipolar diffusion effect.Finally,benefiting from the simultaneous optimization of the electrical and thermal properties,the optimized figure of merit（z T）value of 0.40（increased by～7.0 times）at 723 K was achieved in P-type In_0.93Cd_0.07Sb,which is higher than most state-of-the-art P-type InSb materials.This study could be significant to develop cognate thermostable TE devices by utilizing P-type InSb counterparts.5.The InSb-based solar thermoelectric generators（STEG）are designed and constructed,and the geometric structure of the device was optimized by finite element simulation.It is found that coating the light absorption layer on the surface of the device can effectively improve the photothermal conversion efficiency of the device,increase the temperature difference between the two ends of the device,and obtain higher output voltage.The STEG device coated with a carbon nanotube light absorption layer can achieve an output voltage of 22.2 m V at 10 Sun at room temperature.Due to the high-temperature thermal stability of InSb-based semiconductor materials and the excellent thermoelectric properties at high temperature,it indicates that the photothermal coupling device has a broader application prospect in high-temperature environments with concentrated and intense light.