平面超薄膜结构窄波段热辐射发射特性研究

Thermophotovoltaic holds promise for distributed harvesting of solar energy and industrial wasted heat, but its performance is hindered by poor understanding and manipulation of narrow-band thermal emission. This project studies ultrathin (enriched thermal phenomenon) planar (easy fabrication for practical applications) films instead of sophisticated micro/nano-structures. The first problem is that a two dimensional condition should be satisfied to excite the non-trivial interference resonance in an ultrathin planar film but the film thickness is the only one tunable parameter, so radiative properties significantly rely on intrinsic material properties. To address this issue, the effective medium and phase compensation design methods are developed to provide an extra dimension of freedom to efficiently enhance the narrow-band thermal emission. The second problem is that the non-trivial interference resonance is angle-insensitive for only TE polarization but thermal radiation is unpolarized and hemispherically distributed. Therefore, the dispersion relations of both Brewster and surface waves are investigated using theories of micro/nano-scale thermal radiation, electromagnetism and materials science to understand the coupling mechanism between the non-trivial interference and surface plasmon resonances. A novel scheme is further developed to manipulate emissivity for different angles and polarizations. This project provides theoretical basis for thermophotovoltaic applications.

热光伏是有前景的分布式太阳能和工业余热发电技术，当前面临的工程热物理基础问题是如何高效增强与调控窄波段热辐射发射特性。本课题与依赖复杂微结构设计的传统思路不同，以具有简单平面结构（加工简单廉价、利于工业化生产）且厚度比波长小一个数量级（热科学内涵丰富）的平面超薄膜为对象。通过发展等效介质与相位补偿方法，增加相位匹配的可调控维度，解决非平凡干涉共振效应需满足两个维度的匹配条件与只有一个可调参数的矛盾，突破平面超薄膜结构热辐射特性对材料属性的依赖，以高效增强窄波段热辐射发射特性；运用微纳尺度热辐射学、电磁学和材料学等多学科的基础理论，构建Brewster波与表面波色散关系理论模型，揭示非平凡干涉共振效应与表面等离子共振效应高效耦合的波矢匹配机制，解决非平凡干涉共振效应只对TE波角度变化不敏感与热辐射无偏振及半球空间分布的矛盾，以协同调控发射率的角度与偏振特性。可为热光伏的实际应用提供理论基础。

能量密度低是太阳能利用面临的重要问题之一：大规模利用太阳能发电需要巨大的面积，但最缺电的地方恰恰是可利用占地面积极为有限的城市。现代城市高层建筑林立，太阳照射面积——幕墙面积大，设计颜色美观、可装饰建筑幕墙的太阳能电池，可显著增大太阳能发电面积。彩色太阳能电池研究的传统思路被动依赖半导体材料的固有属性。半导体的本征吸收使电池实际吸收光谱偏离理想光谱，电池颜色暗、不美观。与传统思路不同，本项目采用主动调控吸收光谱的学术思路：减小半导体材料厚度至比波长小一个数量级，抑制材料的本征吸收；激发共振，增强目标光谱的选择性吸收。本项目提出了“超构平面”概念，揭示了超构平面中光-物质相互作用的Brewster共振机理，发展了直接、定量的设计方法，高效增强了厚度比波长小一个数量级的半导体薄膜的吸收特性，建立了兼具波长选择性、广角度和偏振不敏感特性的热辐射吸收原理与方法，解决了传统薄膜结构吸收特性对入射光角度和偏振变化敏感的难题，克服了复杂纳米结构加工困难、成本高的缺点。以超构平面为结构模型，构建了兼具美观与高效的太阳能电池，研制了超构平面太阳能电池的原理器件。本项目研究结果为热辐射特性调控、建筑光伏一体化提供了新思路。