On September 1^st 2023, the Italian Ministry for University and Research has financed the project Active Daytime Radiative Coolers (ARCO), within the framework of the Next Generation EU funding and under the auspices of the “Bando Prin 2022 PNRR”

Passive Daytime Radiative Coolers (PDRCs) are photonic systems that passively achieve sub-ambient cooling even when subjected to direct sunlight illumination [1,2]. PDRCs consist of a combination of an optical layer having high reflectivity in the visible/near infrared (VIS-NIR) range with another optical layer characterized by selective radiation emissivity in the transparency window of the atmosphere, located at 8-13 μm. PDRCs are, by all means, a disruptive technology with tremendous potential for climate mitigation measures [3-8]. Since their introduction in 2014, huge global efforts have been undertaken for optimizing all aspects of PDRCs, from their cooling performance to their durability and fabrication cost [9,10]. One of the greatest improvements still awaiting, however, is the possibility to actively tune the optical response of PDRCs by means of external stimuli, allowing to reversibly switch their optical response between a radiative-cooling or a thermal-absorbing state [11,12]. Such an improvement would allow scientists to make the most of the PDRC performances in a wide range of atmospheric and climatic conditions, ultimately making PDRCs suitable as an energy-saving technology under real-world conditions.

The objective of ARCO is the search and implementation of novel materials and concepts for achieving stimuli-responsive PDRC systems, and the realization of a prototype of active PDRC. The system we propose to achieve this goal is a photonic multilayer composed of a metallic substrate with absorbance in the short-wavelength visible range, topped by an active distributed Bragg reflector (DBR) with voltage-tunable photonic band gap. The two subsystems will be covered by a microstructured polymer-based composite IR-emissive layer. Modulating the photonic band gap of the DBR will allow to mask/unmask the metallic substrate absorption, thereby switching between a state where there is net electromagnetic-energy absorption and a thermal-emissive state, where the system will achieve radiative cooling.

The PI of the project is Dr. Francesco Bisio, Senior Researcher at the CNR-SPIN Institute in Genova. Other institutions involved are the CNR-SCITEC Institute (Dr. P. Stagnaro, Dr. L. Conzatti, Dr. S. Losio) and the Polytechnic of Turin (Prof. F. Scotognella).