Radiative sky cooling reduces the temperature of an object by exchanging heat with the cold universe through the sky. Such radiative cooling mechanism exists in nature but with lower cooling efficiency. For effective radiative cooling, the surface of an object should have high reflectivity in the solar spectrum and high emissivity in Earth's atmospheric transparent window (8-13 µm). In this work, we report a new class of radiative sky cooling material – cellulose-upgraded polymer films. This sample has low absorption in the solar spectrum and high emissivity in the mid-infrared region. When exposed to direct sunlight, this optimized sample cools to 3.97 °C below the ambient temperature and has a cooling power of 82.66 W/m² during the late afternoon. Placing this sample in direct contact with a silicon solar cell shows a reduction in operating temperature under direct sunlight that can enhance the power output from the cell. This approach can easily be applied to large areas at a low cost and is a significant step forward for the large-scale application of radiative cooling technology.

辐射天空冷却通过天空与寒冷的宇宙交换热量来降低物体的温度。这种辐射冷却机制在自然界存在，但冷却效率较低。为实现有效的辐射冷却，物体表面应在太阳光谱中具有高反射率，在地球大气透明窗口 (8-13 µm) 中具有高发射率。在这项工作中，我们报告了一类新的辐射天空冷却材料——纤维素升级聚合物薄膜。该样品在太阳光谱中具有低吸收率，在中红外区域具有高发射率。当暴露在阳光直射下时，这种优化的样品冷却至环境温度以下 3.97 °C，冷却功率为 82.66 W/m ²在下午晚些时候。将此样品与硅太阳能电池直接接触显示在阳光直射下工作温度降低，这可以提高电池的功率输出。这种方法可以很容易地以低成本应用于大面积，是辐射冷却技术大规模应用的重要一步。