温差发电系统中异质材料晶界扩散机理及热电性能优化研究

To solve the key problems of their low thermo-electricity conversion efficiency and short service life of the existing thermoelectric power generator modules, this project will focus on the research of diffusion mechanism of electrode- thermoelectric materials’ grain boundaries and optimization of the thermoelectric power generator performance. First, the diffusion regulation will be obtained at the related interface influenced by different factors such as soldering parameters, working conditions and solders, according to the analysis of the micro morphology and main chemical components. The numerical model will be built to describe the contact behavior at the interface of metal-semiconductor, which is utilized to analyze the stability of chemical reaction allowing for different contact materials. Second, the change law of contact resistance will be obtained in corresponding to the material diffusion process at the related interface by means of contact resistance measurement. Then the main chemical components together with their spatial distributions in the diffusion layer will be measured and manufactured subsequently. According to their specific resistance measured, the internal cause for the contact resistance increase will be revealed. Then a numerical model will be built coupling multi-physics fields including heat, electricity and force as well as multiple effects of thermoelectric materials. The effects of contact resistance on the thermo-electricity conversion efficiency reduction will be figured out. And the influences from diffusion effect on the thermoelectric power generator performance will be then revealed. Finally, some effective strategies will be put forward to inhibit the diffusion of grain boundaries of electrode-thermoelectric materials, and the performance optimization methods will be obtained to promote the thermo-electricity conversion efficiency.

针对现有温差发电组件热-电能量转换效率不高和服役寿命有限的关键问题，本项目拟开展电极-热电材料晶界扩散机理及热电性能优化研究。首先，根据扩散层的微观形貌及主要化学成分分析并获得不同钎焊工艺参数、不同工况、不同焊料因素下电极-热电臂界面扩散规律，明确影响界面扩散作用的主要因素。建立描述金属-半导体界面接触行为的数学模型，分析不同接触材料情况下界面反应的稳定性。其次，通过测量接触电阻获得电极-热电臂界面扩散过程中接触电阻的变化规律，结合界面扩散层中主要生成物及分布特征，制备相应材料并分析其电阻特性，揭示扩散过程中界面接触电阻上升的内在原因。建立基于热电材料多种效应的热、电、力多场耦合数学模型，明确接触电阻在降低热电转换效率中的作用，揭示扩散作用对热电性能的影响机制，最后，针对以上研究结果，提出抑制电极-热电材料晶界扩散作用的有效策略，获取提升热电转换效率的性能优化方法。

针对现有温差发电器件热-电能量转换效率不高和服役寿命有限的关键问题，本项目围绕器件服役特性演变、关键机理及性能优化开展研究工作。首先，根据温差发电器件实际使用工况搭建了具备热、力、电等条件可控的试验测试平台，结合器件多物理场建模对试验测试和仿真准确性进行相互验证，模型偏差小于4%。其次，提出了表征器件中热电材料变物性参数（电导率、热导率和赛贝克系数）的测试新方法-准稳态法，通过进一步改进可实现器件服役过程中晶界接触阻抗的实时测量，相较以往方法大幅提高参数测量的准确性（偏差<12%）和高效性。再次，通过对器件发电性能及晶界微观形貌、化学组分的分析测试，试验发现相较于晶界扩散而言，由于热应力引起器件边缘及端部的微裂纹是导致其性能逐渐下降的主要原因。结合反复试验测试获得了减少器件裂纹发生、提升寿命周期的器件制备工艺与最佳服役工况条件。最后，结合所建立的一维温差发电器件数学模型，将爬坡法引入器件最优结构参数的搜寻算法中，相较于穷举法可大幅提升效率（耗时仅为8.7%）。通过本项目的研究工作，最终提出抑制电极-热电材料晶界扩散作用的有效策略，获得了提升热电转换效率的性能优化方法。