Light angle dependence of photothermal properties in oxide and porphyrin thin films for energy-efficient window applications
Light angle dependence of photothermal properties in oxide and porphyrin thin films for energy-efficient window applications
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DOI：
10.1557/mrc.2020.39
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发表时间：
2020-09
影响因子：
1.9
通讯作者：
Meng-Du Lyu;Jou Lin;J. Krupczak;D. Shi
中科院分区：
文献类型：
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作者：
Meng-Du Lyu;Jou Lin;J. Krupczak;D. Shi
利用模拟太阳光在铁氧化物(Fe_3O_4和Fe_3O_4@Cu2-x S)和卟啉化合物(叶绿素和叶绿素)薄膜上进行了入射光角依赖的光热实验。用不同的溶液方法合成了Fe3O4和Fe3O4@Cu2-x S，得到了10 nm量级的单分散纳米粒子。从新鲜菠菜中提取叶绿素，而叶绿素铜钠是一种商品化产品。这些光热(PT)材料分散在聚甲基丙烯酸甲酯(PMMA)溶液中，通过旋涂在玻璃基板上沉积，得到透明透明的薄膜。铁氧化物薄膜具有明显的吸收光谱，Fe3O4在紫外区有一个较强的吸收峰，并逐渐向可见光和近红外区减弱；Fe3O4@Cu2-x S在紫外区的吸收相似，但在近红外区表现出较宽的吸收。叶绿素和叶绿素的特征是在UV和NIR附近有吸收峰，呈现“U”形光谱，这是高效太阳能收集和节能单窗应用中高透明度所必需的。在窗口内表面涂覆透明的PT薄膜时，太阳辐射会诱导光热效应，从而提高薄膜的温度。以这种方式，基于所谓的光学隔热(OTI)的新概念，通过减少窗户内表面和房间内部之间的温差，可以显著降低通过窗户的热损失，而不需要如玻璃技术中所要求的任何干预介质，例如空气/Ar。因此，单格可以取代双格或三格格。由于OTI不可避免地受到季节和每日阳光变化的影响，因此光热效应的入射光角关系在薄膜和窗口设计中都是至关重要的。结果表明，在小角度入射时，加热曲线出现极大值，而在大角度时，光热效应明显减弱。这种角度依赖关系被薄膜表面的光反射很好地解释了，然而，由于衬底的非理想表面，偏离了菲涅耳定律的预测。角度相关性数据为OTI提供了一个重要的参考资料，即冬至时窗户对太阳的曝光量较大，而夏季窗户对太阳的曝光量较小。这一结论表明，冬季通过光学隔热窗大大增强了太阳能的收集和热转换，导致了低得多的U因子。
The photothermal experiments on the incident light angle dependence are carried out using simulated solar light on thin films of both iron oxides (Fe_3O_4 and Fe_3O_4@Cu_2- x S) and porphyrin compounds (chlorophyll and chlorophyllin). Fe_3O_4 and Fe_3O_4@Cu_2- x S are synthesized using various solution methods that produce mono-dispersed nanoparticles on the order of 10 nm. Chlorophyll is extracted from fresh spinach and chlorophyllin sodium copper is a commercial product. These photothermal (PT) materials are dispersed in polymethyl methacrylate (PMMA) solutions and deposited on glass substrates via spin coating that result in clear and transparent thin films. The iron-oxide based thin films show distinctive absorption spectra; Fe_3O_4 exhibits a strong peak near UV and gradually decreases into the visible and NIR regions; the absorption of Fe_3O_4@Cu_2- x S is similar in the UV region but shows a broad absorption in the NIR region. Both chlorophyll and chlorophyllin are characterized with absorption peaks near UV and NIR showing a “U”-shaped spectrum, ideally required for efficient solar harvest and high transparency in energy-efficient single-pane window applications. Upon coating of the transparent PT films on the window inner surfaces, solar irradiation induces the photothermal effect, consequently raising the film temperature. In this fashion, the thermal loss through the window can be significantly lowered by reducing the temperature difference between the window inner surface and the room interior, based on a new concept of so-called optical thermal insulation (OTI) without any intervention medium, such as air/argon, as required in the glazing technologies. Single-panes are therefore possible to replace double- or triple panes. As OTI is inevitably affected by seasonal and daily sunlight changes, an incident light angle dependence of the photothermal effect is crucial in both thin film and window designs. It is found that the heating curves reach their maxima at small angles of incidence while the photothermal effect is considerably reduced at large angles. This angle dependence is well explained by light reflection by the thin film surface, however, deviated from what is predicted by the Fresnel's law, attributable to non-ideal surfaces of the substrates. The angle dependence data provide an important reference for OTI that window exposure to the sun is greater at winter solstice while that is considerably reduced in the summer. This conclusion indicates much enhanced solar harvesting and heat conversion via optically insulated windows in the winter season, resulting in much lower U -factors.