We theoretically analyze the impact of angular selectivity on the radiative cooling performance of thermal emitters. We investigate the effect of spectral selectivity, environmental conditions, and parasitic heating on the minimum possible equilibrium temperature of the thermal emitter. We show that combining angular and spectral selectivity is necessary to reach deep subfreezing temperatures. We also show that angularly selective thermal emitters increase the cooling performance in humid environments, however, they require management of nonradiative heat transfer processes. We introduce a general scheme to realize angularly and spectrally selective absorption/emission using a thin film stack consisting of an angle dependent transmission filter overlayed on a selective thermal emitter. The thermal emitter total thickness is ∼16 μm, an order of magnitude less than previously proposed angular selective thermal emitters/absorbers and operates under s- and p-polarized light without using anisotropic layers. Under realistic conditions and reasonable parasitic heating, the proposed emitter can be cooled down to ΔT = −46 °C below ambient temperature. Our work highlights the advantages and drawbacks of angular selective thermal emitters towards practical and efficient radiative cooling devices.

中文翻译：

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用于深度低于冰点的白天辐射冷却的角度选择性热发射器

我们从理论上分析了角度选择性对热发射器辐射冷却性能的影响。我们研究了光谱选择性、环境条件和寄生加热对热发射器的最低可能平衡温度的影响。我们表明，结合角度和光谱选择性对于达到冰点以下的温度是必要的。我们还表明，角度选择性热发射器可提高潮湿环境中的冷却性能，但是，它们需要管理非辐射传热过程。我们介绍了一种通用方案，使用由覆盖在选择性热发射器上的角度相关透射滤光片组成的薄膜堆栈来实现角度和光谱选择性吸收/发射。热发射器总厚度为~16μm，比先前提出的角度选择性热发射器/吸收器小一个数量级，并且在不使用各向异性层的情况下在 s 和 p 偏振光下工作。在现实条件和合理的寄生加热下，所提出的发射器可以冷却到 Δ吨= -46 °C 低于环境温度。我们的工作突出了角度选择性热发射器对实用且高效的辐射冷却装置的优缺点。