Radiative cooling is a passive cooling strategy with zero consumption of electricity, and it can be used to radiate heat from buildings to reduce air conditioning requirements. Although this technology can work well during optimal atmospheric conditions at nighttime, it is essential to achieve efficient cooling during daytime when peak cooling demand actually occurs. In this article, we report an inexpensive planar polydimethylsiloxane (PDMS)/metal thermal emitter, i.e., a thin film structure, which was fabricated using a fast solution coating process that is scalable for large area manufacturing. By performing tests under different environmental conditions, temperature reductions of 9.5 °C and 11.0 °C were demonstrated in the laboratory and outdoor environment, respectively, with an average cooling power of ~120 W/m 2 for the thin film thermal emitter. In addition, a spectral-selective structure was designed and implemented to suppress the solar input and control the divergence of the thermal emission beam. This enhanced the directionality of the thermal emissions, so the emitter's cooling performance was less dependent on the surrounding environment. Outdoor experiments were performed in Buffalo NY realizing continuous allday cooling of 2~9 °C on a typical clear sunny day at Northern United States latitudes. This practical strategy that cools without electricity input could have a significant impact on global energy consumption.

Abstract100% efficiency is the ultimate goal for all energy harvesting and conversion applications. However, no energy conversion process is reported to reach this ideal limit before. Here, an example with near perfect energy conversion efficiency in the process of solar vapor generation below room temperature is reported. Remarkably, when the operational temperature of the system is below that of the surroundings (i.e., under low density solar illumination), the total vapor generation rate is higher than the upper limit that can be produced by the input solar energy because of extra energy taken from the warmer environment. Experimental results are provided to validate this intriguing strategy under 1 sun illumination. The best measured rate is ≈2.20 kg m−2 h−1 under 1 sun illumination, well beyond its corresponding upper limit of 1.68 kg m−2 h−1 and is even faster than the one reported by other systems under 2 sun illumination.

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waveguides [5] and slow light systems [6] that are insensitive to imperfections. Therefore, it is generally believed that topological effects promise to result in robust and unique designs and functionalities for future photonic systems. "Topological darkness" is a phenomenon described in the 2D optical-constant space (i.e., refractive index, n, and extinction coefficient, k) using the geometric topological concept. [7,8] To distinguish it from other topological photonic structures designed in wave-vector spaces, [3,4] we will refer to it as dispersion topological darkness (DTD) in this article.Perfect/complete suppression of reflection, as one of the prerequisites to enhance the absorption, was explored extensively using various structures. [9,10] It is in principle achievable in several ideal optical systems under given incident angles, polarization states, and wavelengths [e.g., Brewster angle, [11] prism coupled surface plasmon resonance (SPR) system, [12] coherent absorption system, [13,14] and parity-time metamaterial systems [15,16] , complete suppression of reflection is still challenging due to inhomogeneity, disorder or irregularities of samples, and fabrication errors (e.g., inevitable surface roughness). In particular, if the transmission of a structure is further entirely suppressed, along with the complete suppression of reflection in previously reported DTD phenomena, the perfect/ complete absorption can be guaranteed.According to the Fresnel reflection coefficient for a simple three-layered structure (constructed by a top nanopatterned thin-film with engineerable optical constants, a central lossless spacer layer and a bottom mirror to prevent transmission, see the inset in Figure 1a), a zero reflection line divides the finite optical constant (i.e., n and k) 2D space into two regions (see the solid red curve in Figure 1a). If two endpoints of the dispersion curve for a given top nanopatterned thin film locate in these two regions in this closed finite space (see the blue dotted line in Figure 1a), respectively, Jordan theorem [17] secures at least one intersection point between the zero reflection line and the dispersion curve of the top thin film. Therefore, the condition for zero reflection can always be topologically protected within this closed finite space, which is so called "topological darkness." [7,8] This concept is only related to the effective dispersion Complete suppression of reflection is in principle achievable in ideal optical systems with unique optical features including complete light absorption, abrupt phase change, etc. However, conventional optical systems have an extremely tight tolerance on fabrication errors or inherent roughness of thin films or patterns. Therefore, it is difficult to realize the perfect reflectionless condition in practice. To overcome this challenge, a "topological darkness" concept with mild restrictions to the film quality is proposed using periodic metallic patterns and self-assembled core-shell particles. Due to the topological effect, the robust ...

Chiral light‐matter interaction in plasmonic metamaterials represents a new paradigm in optics. However, most previously reported works require structural chirality based on asymmetric three‐dimensional architectures, imposing a significant cost barrier in scalable manufacturing. Here, the generation of superchiral light‐matter interaction in symmetric metal‐dielectric‐metal (MDM) metamaterial structures is theoretically proposed. Due to the interplay of the spatially separated and enhanced electric (E‐) and magnetic (H‐) fields with complementary profiles, a superchiral localized hotspot can be generated in MDM structures when an appropriate phase condition is satisfied. By introducing chiral molecules into the spacer layer, the circular dichroism (CD) signal of the coupled system can be enhanced significantly. The origin of the enhanced CD is attributed to the inherent and induced CD signals of the coupled system, which are derived from the direct molecular CD response and the asymmetric absorption of circularly polarized light by the metallic nanostructure. It is demonstrated that the metamaterial‐induced CD response contributes dominantly to the overall CD response of the coupled system, and a 1300‐fold enhancement factor can be obtained when on‐resonance chiral molecules are adsorbed in the optical superchiral field in the spacer layer. This finding paves the way toward the development of practical and scalable platforms for new chiroptical applications.