Free-standing, colored, polymer film with composite opal photonic crystal structure for efficient passive daytime radiative cooling

Flexible Photonic Radiative Cooling Films: Fundamentals, Fabrication and Applications

“…Similarly, Zhao et al prepared the TiO 2 skeleton by using self-assembled PS spheres. [116] In order to obtain a flexible and freestanding radiative cooling film, the PDMS solution is used to spin-coat the TiO 2 skeleton. Thanks to the meticulously designed fabrication process, the film has been endowed with diverse colors while concurrently maintaining a commendable degree of radiative cooling efficacy.…”

“…In the work of Zhao et al., a 3D TiO 2 skeleton with an anti‐opal structure was designed to obtain reflective full colorization. [ 116 ] By regulating the size of the pores, different Bragg reflections are excited, thus enabling color tailoring. At the same time, the embedded TiO 2 skeleton nanostructures and the evitable vacancy defects or cracks serve to significantly scatter any superfluous visible light, effectively reducing any solar energy absorption.…”

Colored Polymeric Films with a Bilayer Porous Design for Efficient Subambient Radiative Cooling

“…Additionally, a white or silvery appearance may not be desirable in all applications from an esthetic standpoint. To address these challenges, there is a growing interest in the development of colored passive radiative coolers (CPRCs) that simultaneously satisfy the need for colored surfaces and cooling effects. ,, Photonic crystals, multilayer structures, quantum dot materials, and three-dimensional periodic structures are among the commonly employed approaches. − However, despite their thermal performance, most of these strategies require precise fabrication techniques, specialized equipment, complex structures, and high preparation costs, limiting their industrial production and large-scale applications. ,,, Therefore, it is crucial to develop strategies that enable facile and scalable fabrication, esthetic appeal, and high cooling efficiency.…”

Vivid Colored Cooling Structure Managing Full Solar Spectrum via Near-Infrared Reflection and Photoluminescence

“…In principle, coloration results in absorption of a part of the visible (VIS) spectrum (0.4 μm ≤ λ ≤ 0.7 μm); consequently, color representation and RC performance are inversely related. − To resolve this issue, two strategies have been employed for colored RC (CRC). First, enhancing the near-infrared (NIR) reflection does not influence the color representation and can improve the CRC performance. − This was first theoretically and experimentally demonstrated by Wei et al with a pink-colored photonic multilayer structure, showing a temperature difference of 47.6 °C between the structure with low NIR reflection (0.7 μm ≤ λ ≤ 2.5 μm) and another with high NIR reflection . Chen et al proposed a bilayer structure composed of an NIR-reflective hierarchically porous poly­(vinylidene fluoride- co -hexafluoropropylene) (P­(VDF-HFP)) bottom layer and a commercial paint top layer.…”

“…As the top layer does not absorb solar flux in NIR region, the transmitted solar flux within the NIR regime can be reflected by the bottom layer such that the temperature of the bilayer structure could be reduced via pumped NIR reflection . Moreover, theoretically designed multilayer structures that induce Tamm resonance and a Fabry–Pérot structure can be used to obtain cyan-, magenta-, and yellow-colored RCs exhibiting high NIR reflectance ( R NIR ). , Furthermore, structural coloration using periodic opal structures and chiral cellulose have been employed in CRC structures, wherein their color depends on the optical resonance caused by the structural geometry. − However, these approaches are limited because a complex fabrication process is required for structural coloration or vacuum deposition of multiple layers, thereby hindering the scalability and applicability of CRC. Furthermore, the colors had to be relatively light to achieve an affordable CRC performance, as any absorbed sunlight would result in an increase in temperature .…”