We demonstrate a simple, low-cost, and passive radiative cooler based on a monolithic design consisting of thin nanoporous anodic alumina (NAA) films grown on aluminium sheets. The NAA/Al structure maintains a high broadband reflectivity close to 98\(\%\) within the solar spectrum (0.4–2.2 \(\mu \)m) and simultaneously exhibits a high average emissivity of 88\(\%\) within the atmospheric infrared (IR) transmission window of 8–13 \(\mu \)m with the peak IR emission approaching 99\(\%\) at a wavelength of 10 \(\mu \)m. Optical modelling of the system using optical parameters of the materials confirms that the high solar reflectance arises due to the transparent nature of NAA and high reflectivity of bottom Al, while the large thermal IR emissivity arises from the interference effects of the NAA film and the high absorption of IR light due to phonon resonances in alumina at wavelength larger than 10 \(\mu \)m. Further, we estimate the average cooling power of NAA/Al to be about 136 W \(\hbox {m}^{-2}\) at ambient temperature even after including the contribution to heat input from external non-radiative processes. This robust and lightweight NAA/Al can be projected as an excellent alternative to optical solar reflectors used in spacecraft for thermal heat management and rooftop cooling green technologies.

我们演示了一种简单的，低成本的无源辐射冷却器，该冷却器基于整体设计，该设计包括在铝板上生长的纳米多孔阳极氧化铝（NAA）薄膜。NAA / Al结构在太阳光谱（0.4–2.2 \（\ mu \） m）内保持接近98 \（\％\）的高宽带反射率，并同时具有88 \（\％\）的高平均发射率。在8–13 \（\ mu \） m的大气红外（IR）传输窗口内， 在10 \（\ mu \）的波长下，峰值IR发射接近99 \（\％\）米 使用材料的光学参数对系统进行的光学建模证实，由于NAA的透明性和底部Al的高反射率而产生了高的太阳反射率，而较大的热IR发射率则是由于NAA膜的干扰效应和高的红外辐射率引起的。 IR光的吸收是由于氧化铝的声子的共振波长处大于10 \（\亩\）米。此外，我们估计NAA / Al的平均冷却功率约为136 W  \（\ hbox {m} ^ {-2} \）即使包括外部非辐射过程对热量输入的贡献后，也能保持在室温下。这种坚固而轻巧的NAA / Al可以作为航天器中用于热热管理和屋顶冷却绿色技术的光学太阳反射镜的绝佳替代品。