A Self‐Assembled 2D Thermofunctional Material for Radiative Cooling

Abstract The regulation of temperature is a major energy‐consuming process of humankind. Today, around 15% of the global‐energy consumption is dedicated to refrigeration and this figure is predicted to triple by 2050, thus linking global warming and cooling needs in a worrying negative feedback‐loop. Here, an inexpensive solution is proposed to this challenge based on a single layer of silica microspheres self‐assembled on a soda‐lime glass. This 2D crystal acts as a visibly translucent thermal‐blackbody for above‐ambient radiative cooling and can be used to improve the thermal performance of devices that undergo critical heating during operation. The temperature of a silicon wafer is found to be 14 K lower during daytime when covered with the thermal emitter, reaching an average temperature difference of 19 K when the structure is backed with a silver layer. In comparison, the soda‐lime glass reference used in the measurements lowers the temperature of the silicon by just 5 K. The cooling power of this simple radiative cooler under direct sunlight is found to be 350 W m −2 when applied to hot surfaces with relative temperatures of 50 K above the ambient. This is crucial to radiatively cool down devices, i.e., solar cells, where an increase in temperature has drastic effects on performance.