Accelerating the discovery of multilayer nanostructures with analytic differentiation of the transfer matrix equations

Abstract

Multilayer nanostructures represent an important class of materials with tunable optical and thermal radiative properties that can be leveraged for a wide range of energy applications. We present a theoretical framework for optimizing the geometry of such structures that utilizes gradients of various objective functions that are enabled through analytic differentiation of the transfer-matrix equations. We demonstrate the usefulness of this method by applying it to the local optimization of many-degree-of-freedom structures for incandescent light sources, and the global optimization of few-degree-of-freedom structures that serve as solar cell coatings and optical cavities for enhancing the absorption of organic chromophores embedded in thin films.

Spectral Regulation in Thermophotovoltaic Devices

“…7 Optical properties of the intrinsic selective emitters: (a) Comparison of radiation intensity between Yb2O3 selective thermal emitter and 1735K blackbody [52] ; (b) Comparison of radiation intensity between Er2O3 selective thermal emitter and 1735K blackbody [52] . Fano 干涉增透膜的机制最早由斯坦福大学的 Shanhui Fan [19] 与荷兰原子与分子物理研究所的 Albert Polman [58] 确立。Shemelya 等 [59] 首次将这一机制应用于热光伏电池，在 GaSb 光伏电池的上表面沉积 Au 亚波长网格结构。 Au 亚波长网格结构不仅可以作为 Fano 干涉增透膜，还可作为电极替代光伏电池的叉指电极。这一设计同时提 升了超带隙波段透光率与电极的电导率，大幅提升了光电流。Zhang 等 [60] 通过时域有限差分法讨论了不同形状的 空腔对于光栅性能的影响，发现六边形蜂巢形状的光栅具有最高的超带隙透光率以及亚带隙反射率。同时，较高 的光栅结构有助于减少入射光子的散射，可进一步提升 TPV 器件的效率。 一维光子晶体 DBR 滤波器利用具有高折射系数与低折射系数的材料叠层构成的光子禁带来反射亚带隙的 热辐射光子。 一维光子晶体 DBR 滤波器通常由非氧化物介电材料构成， 以避免中红外波段的声子激元发射损耗。 早期研究中，高折射系数材料通常选用 Sb2Se3，而低折射系数材料通常选用 YF3。Gratrix 等 [61,62] 采用双层串联 结构对入射光谱进行调控，即在等离激元滤波器上沉积 Sb2Se3-YF3 干涉滤波器构成串联光滤波器结构。Sb2Se3-YF3 干涉滤波器可反射 2~6 μm 的光子，而等离激元滤波器可反射更长波段的光子。但非垂直入射条件下 Sb2Se3-YF3 一维 DBR 滤波器会发生近红外 0.72~2.5 μm 波段显著的吸收，导致带内光子密度减少，输出功率降低。 上述一维光子晶体 DBR 滤波器均直接沉积在光伏电池的表面。Bierman 等 [63] 将滤波器与光伏电池分离，利 用商用梳齿型啁啾滤波器成功抑制了 80%的带隙能量以下的热辐射光子，基于此搭建的 TPV 示意图如图 8(a) 所示。由于梳齿型啁啾滤波器多为复杂的非周期结构，因此对结构设计提出了巨大挑战。随着人工智能技术的发 展，借助算法对滤波器结构进行优化可以实现更优异的光学性能。Varner 等 [64] 对固定层数与材料的多层结构进 行优化，并通过传递矩阵方程的解析微分获得目标函数的梯度。与数值微分方法相比，传递矩阵法能够更加精确 地计算出结构的光学性能。Jiang 等 [65] 基于 ResNet 神经网络，完成了一维多层结构的多目标分类全局优化，如图…”

Twenty years of exceptional success: The molecular education and research consortium in undergraduate computational chemistry (MERCURY)

“…Key scientific outcomes so far include the discovery of an emergent optical phenomenon in composite nanoparticles known as “scattering‐mediated absorption”, [ 456–458 ] and the development of an open‐source software package, WPTherml, for designing materials for harnessing heat. [ 459,460 ]…”

A photon-recycling incandescent lighting device

“…Furthermore, as the majority of the emitted power from the tungsten filament is in the infrared range, the luminous efficacy of the incandescent lighting remains below 15 lumens (lm)/W (luminous efficiency <2%), which is much lower than that of the SSL (luminous efficacy > 100 lm/W). Previous conceptual demonstration of tailoring thermal radiation using photonic crystal or interference filter (14)(15)(16)(17) increases the luminous efficacy of the incandescent lighting to 45 lm/W (efficiency of 6.6%), which is still far inferior to those of the state-of-the-art SSL (140 to 160 lm/ W) (13). Besides, the lifetime issue of the tungsten filament remains unsolved.…”