调节纳米阴极能带结构实现中低温高效真空热电转换研究

Thermionic conversion is an important approach to realize efficient energy conversion and show greatly potential application in efficient energy conversion especially in waste heat recovery field. Refractory metal has been used as the cathode in traditional thermionic conversion, high efficiency could be achieve at high temperature (>50%). How to achieve high conversion efficiency in moderate temperature (500-700 K) is the key to realize the practical application of thermionic conversion. By combining the defect-enhanced thermal emission phenomenon of low-dimensional semiconductor nano-cathode discovered in our early studies with the modification of surface energy band structure, an assumption of achieving high-efficiency thermionic conversion at moderate temperature was proposed in this project to solve the problem of realizing the application of thermionic conversion in waste heat recovery field. Thermionic conversion model considering defect, size effect and Joule heating for low-dimensional semiconductor nanomaterials will be established first. Under the guidance of the model, relationship between the electronic band structure, temperature and conversion efficiency will be expounded theoretically and experimentally. Further, effective approaches to modulate the electronic band structure of the low-dimensional semiconductor nanomaterials in order to obtain high conversion efficiency will be explored. A method to study the electronic band structure of nanowires by combining in-situ microstructure characterization, temperature-dependent carrier mobility measurement, and variation of the carrier concentration at different temperature measured by s-SNOM will be developed. This project is expected to make breakthroughs in thermionic conversion mechanism and the application of thermionic conversion devices, which is of great significance for the efficient utilization of energy.

真空热电转换是实现高效能量转换的重要途径，在能量转换特别是余热回收领域具有重要应用前景。传统真空热电转换采用难熔金属阴极，高温下才可实现高效率（>50%），如何在中低温（500-700 K）实现高效率是真空热电转换实用化的关键。本项目提出利用我们前期发现的低维半导体纳米阴极缺陷辅助热发射现象结合表面能带结构调节，实现中低温下真空高效率热电转换的设想，以解决其在余热回收实现应用的难题。项目首先建立系统考虑缺陷、尺寸、焦耳热等影响的低维半导体纳米材料真空热电转换模型。再结合模型，从理论和实验上阐明能带结构变化与温度及转换效率的关系，探讨如何有效调节能带结构，以实现中低温高效率转换。拟发展结合原位微观特性表征、变温载流子迁移率表征、s-SNOM载流子浓度表征等的方法，提取阴极能带信息，并研究其对转换效率的影响。本项目工作有望在新型真空热电转换机制及其器件应用取得突破，对高效利用能源具有重要意义。

真空热电转换可实现高效能源利用，半导体纳米材料电子发射具有明显的温度效应，有望实现高效热电转换，具有重要研究意义。本项目以提高热电转换效率为目标，采用半导体纳米材料和包覆型半导体纳米材料两种材料体系，围绕调节半导体纳米材料能带结构实现中低温高效真空热电转换的关键科学问题开展研究。首先系统研究了半导体纳米线的电学性质和场发射特性，建立了考虑缺陷的半导体纳米线输运和场发射电流理论模型，提出一种缺陷辅助场发射模型。进一步地，我们建立了考虑缺陷的半导体纳米材料的真空热电子发射模型、考虑缺陷及电子发射过程中的焦耳热的半导体纳米材料的光子增强热电子发射模型以及包覆型半导体纳米材料的光子增强热电子发射模型，讨论热电转换效率的影响因素。最后，我们通过调节纳米材料的缺陷浓度，研究其电子发射特性并验证模型。此外，还建立真空红外热电/光电能量转换研究装置，为研究纳米阴极光热电转换特性提供支撑，探索了部分材料在阴极电子源、能量转换器件中的应用。