Subambient daytime radiative cooling enables temperatures to passively reach below ambient temperature, even under direct sunlight, by emitting thermal radiation toward outer space. This technology holds promise for numerous exciting applications. However, previous demonstrations of subambient daytime radiative cooling require surfaces that directly face the sky, and these cannot be applied to vertical surfaces that are ubiquitous in real-world scenarios such as buildings and vehicles. Here, we demonstrate subambient daytime radiative cooling of vertical surfaces under peak sunlight using a hierarchically designed, angularly asymmetric, spectrally selective thermal emitter. Under peak sunlight of about 920 watts per square meter, our emitter reaches a temperature that is about 2.5°C below ambient temperature, corresponding to a temperature reduction of about 4.3° and 8.9°C compared with a silica-polymer hybrid radiative cooler and commercial white paint, respectively.

中文翻译：

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垂直表面的低于环境日间辐射冷却


低于环境的日间辐射冷却通过向外太空发射热辐射，使温度能够被动地低于环境温度，即使在阳光直射下也是如此。这项技术有望为许多令人兴奋的应用带来希望。然而，以前的亚环境日间辐射冷却演示需要直接面向天空的表面，而这些表面不能应用于在实际场景中无处不在的垂直表面，例如建筑物和车辆。在这里，我们展示了在峰值阳光下垂直表面的亚环境日间辐射冷却，使用分层设计、角度不对称、光谱选择性的热发射器。在每平方米约 920 瓦的峰值阳光下，我们的发射器温度比环境温度低约 2.5°C，与二氧化硅-聚合物混合辐射冷却器和商用白色涂料相比，温度分别降低了约 4.3°C 和 8.9°C。