The passive radiative cooling approach refers to the physical process that pumps heat into outer space via the atmospheric window (8–13 μm) without energy input. The ability to continuously adjust the emissivity of thermal emitters in the sky window while maintaining high reflectivity in the solar spectrum remains a challenge. In order to achieve this task, a novel design referred to as double-layer nanoparticle-based coating is proposed. Our proposed emitter is appropriate for both high solar reflection and strong mid-infrared emissivity. The bottom and top layers are Al₂O₃ embedded with Ni nanoparticles and a super-hydrophilic TiO₂-SiO₂ layer. The bottom layer is designed to achieve high emissivity in “the atmospheric transparency window”. The top layer is designed to block solar illumination and to favor an enhanced cleanability of the coated design. Our double-layer coating as an optical solar reflector has excellent solar irradiation ($0.96$) and is strongly emissive (0.97) across the “full sky window” at room temperature. Furthermore, a detailed numerical energy study has been performed, evaluating the temperature reduction and the radiative cooling performance under different conditions. The proposed simple coating can be used as an efficient radiative cooler on a large scale for energy conservation and thermoelectric devices.

中文翻译：

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用于高效日间和夜间辐射冷却的简单双层涂层

被动辐射冷却方法是指在没有能量输入的情况下通过大气窗口（8-13μm）将热量泵入外层空间的物理过程。在保持太阳光谱中的高反射率的同时，不断调整天空窗口中热发射器的发射率仍然是一个挑战。为了完成这项任务，提出了一种称为双层纳米颗粒涂层的新型设计。我们提出的发射器适用于高太阳反射和强中红外发射率。底层和顶层是嵌入了 Ni 纳米颗粒和超亲水性 TiO ₂ -SiO _{2 的}Al ₂ O ₃层。底层旨在在“大气透明度窗口”中实现高发射率。顶层设计用于阻挡阳光照射并有利于增强涂层设计的可清洁性。我们的双层涂层作为光学太阳能反射器具有出色的太阳辐射（$0.96$) 并且在室温下在“全天窗”上具有强发射 (0.97)。此外，还进行了详细的数值能量研究，评估了不同条件下的温度降低和辐射冷却性能。所提出的简单涂层可用作大规模的高效辐射冷却器，用于节能和热电设备。