二维层状材料中电-声子耦合对热电性能的调控

At present, the energy crisis is a well-known global issue. The key for solving this problem is to develop and explore new sustainable green-energy. Thermoelectrics converts waste heat into useful electricity. The ideal thermoelectric materials should have the electrical conductivity and the Seebeck coefficient as high as possible, but keep the thermal conductivity as low as possible. However, due to the correlation of electron and phonon transport, the three coefficients are not independent. Therefore, it is important to evaluate correctly and deeply the effect of electron-phonon coupling on the figure-of-merit zT for improving the efficiency of thermoelectric conversions. In this project, based on first-principles calculations and taking the electron-phonon interactions into account, we plan to investigate the thermoelectric transport properties in two-dimensional layered materials. On the other hand, as increasing temperatures, the electron-phonon interactions are enhanced. Therefore, we are also going to discuss the effect of temperature on the energy band and transport properties. We will mainly focus on the semiconducting layered materials composed by the groups IV, V and VI elements and some transition metal dichalcogenides. We expect to disentangle the role of electron-phonon coupling on the thermoelectric performance with respect to either positive or negative effects. Our studies act as an important reference for designing novel thermoelectric devices.

目前能源危机是一个众所周知的全球性难题，而开发和探索可持续使用的绿色新能源是解决本难题的关键。热电转换就是将废弃的热能转换成可用的电能。最理想的热电材料应该使电导和塞贝克系数尽量大，而使热导尽量小。然而由于电子与声子输运的相互关联，这三者并不能独立地变化。因此，正确和深刻地评估电-声子相互作用对热电优值zT的调控对提高热电转换效率至关重要。在本项目中，我们计划基于第一性原理方法，考虑电-声子耦合效应，研究二维层状材料的热电输运性质。另外，温度的升高会加强电-声子耦合效应。因此，我们也将讨论温度对层状材料能带及输运性质的调控作用。我们将主要聚焦在由IV、V、和VI主族元素组成的层状材料和一些过渡金属硫化物。我们期望能阐明电-声子耦合对热电性能的积极与消极作用，从而为设计新型的热电器件提供依据。

热电材料将热能转换成电能具有广阔的实际应用前景。为了提高热电转换效率，揭示调控半导体热电转换的关键因素对热能利用和器件设计至关重要。自本项目立项以来，我们主要聚焦在阐明电-声子相互作用调控二维层状材料热电性能物理机制，取得的成果主要包括：研究了强层间耦合材料的热电性能，揭示了其内在的物理机制；研究了二维和三维硼化物的声子热导率，阐明了其反常热导率的机理；研究了铜基材料、铅硫族化合物极低热导率的物理起源，提出了原子轨道耦合模型；解释了传统半导体在低温下出现负热膨胀的原因；提出了计算低维体系在热激发状态下带电缺陷性质的新方法，并系统研究了替位、空位等缺陷对材料导电性的影响；讨论了半导体能带对齐及其在光电器件方面的重要应用；计算了激子结合能，开展了能谷电子学、钙钛矿等有关的研究。这些研究为设计热电能源器件提供了重要的理论支撑。此外，在该项目的支持下，我们与国内外一些知名课题组建立了深入的合作关系，多次参加学术会议，已发表SCI论文12篇，另外4篇正在投稿和评审中，PR系列3篇，影响因子大于25的论文1篇。财务方面严格按照预算和相关规定进行。人才培养方面参与研究的三名学生中，其中两人已获得博士学位，一人获得硕士学位。