Porous block copolymer films with self-adjustable optical transmittance and passive radiative cooling

As an energy-free cooling technique, radiative cooling has garnered significant attention in the field of energy conservation. However, traditional radiative cooling films often possess static optical properties and their inherent opacity limits their applications in building such as windows. Therefore, there exists a requirement for passive radiative cooling films endowed with adjustable transmittance. Here we report the porous block copolymer films with self-adjustable optical transmittance and passive radiative cooling. In a result, the film exhibited a high solar reflectance (0.3–2.5 μm) of 96.9% and a high infrared emittance (8–13 μm) of 97.9%. Outdoor experiments demonstrated that the film surface temperature was 6.6 °C lower than ambient temperature, with a cooling power of 104.8 W·m^–2. In addition, the film’s transmittance can be regulated by altering the polarity of the post-processing solvent, providing an effective approach for regulating indoor light intensity and thermal balance, thereby enhancing the applicability of radiative cooling.