We report an ultrabroadband perfect metamaterial absorber, comprising a two-dimensional array of a hemi-ellipsoid shaped metallo-dielectric multilayered structure. What we believe, to the best of our knowledge, is an unprecedented average absorbance of ∼ 99 % is theoretically demonstrated in the 300 to 4500 nm spectral range at normal incidence. We use 20 pairs of molybdenum–germanium metallo-dielectric layers with tungsten as the ground metal placed on a silicon substrate. Our design is polarization-independent as well as angle-insensitive (up to 60°), making it a perfect “superabsorber.” Theoretical modeling based on effective medium theory validates our full-wave simulation results. The figure-of-merit calculations suggest that our superabsorber can outperform recently reported broadband absorbers. The proposed design has potential application in thermophotovoltaics for solar energy harvesting.

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We propose low-power designs of electrotunable absorption- and transmission-mode color filters and optical switches based on a metal–dielectric–metal structure. By applying voltage across an electro-optic polymer, used as a dielectric layer, tunable color filtering is achieved over a voltage range of − 10 V to + 10 V . Moreover, by adjusting each layer thickness, such designs can also be used as optical switches at 1550 nm telecom wavelength, exhibiting unmatched ∼ 99 % switching efficiency, operable with only 5 V power supply. Our theoretical results agree well with full-wave simulations. Our design is lithography-free, large-area compatible, power-efficient, polarization-independent, and angle-insensitive and has an extremely narrow bandwidth (12 nm).

Passive all-weather windows, capable of selectively transmitting visible and infrared solar radiation, could help in bringing down fossil-fuel energy consumption globally by reducing the carbon footprint of typical air-conditioning systems for buildings and motor vehicles. Here, we report on designing metal–insulator–metal thin-films for application in passive windows, optimized for different climatic conditions. We analyze designs comprising different noble metals as well as their relatively inexpensive alternatives. By finding an optimal choice of materials and thicknesses of the metal and dielectric layers, our lithography-free simple design can provide all-weather solutions for passive windows with desired visible and infrared transmission/blocking capability. Obtained theoretical results agree well with full-wave simulations. Thus, our proposed designs enable developing low-cost, ultra-thin (thickness: 47–85 nm), polarization-independent, angle-insensitive (up to 83 deg), and large-area-compatible passive windows with improved solar-radiation control for different weather/climatic conditions. The figure-of-merit calculation shows that the relatively inexpensive metals used in our passive glasses can outperform industry-standard commercial glasses and previously reported infrared-blocking plasmonic glasses.

Passive radiative coolers (PRCs), which pump excess heat to cold exterior space via thermal radiation, have emerged as a promising energy-free technology in cooling buildings, thermal power plants, and photovoltaics. However, designing a ‘daytime’ PRC is challenging due to the simultaneous requirement of high reflectance in the solar spectral regime (0.3–2.5 µm) and high emissivity in the atmospheric transmittance window (8–13 µm). Here, we present a large-area compatible and lithography-free nanoscale multilayer design of daytime PRC based on two pairs of tandem silicon dioxide–aluminium nitride dielectric layer cascaded to a silver ground metal placed over a silicon substrate. We theoretically achieve near-perfect reflectance (97.3%) over the solar spectral regime while maintaining high emissivity (80%) in the atmospheric transmittance window. During the daytime under direct sunlight, the cooling power of the proposed structure is reported to be 115 W m − 2 with a temperature reduction up to 15 K below the ambient temperature, when the effect of convection and conductive heat transfer is considered. Our design is polarization-independent and angle-insensitive up to 70 degrees of angle of incidence. An excellent match between our theoretical and simulation results validates our findings. The fabrication tolerance study reveals that the cooling performance of our robust design is unlikely to degrade much during experimental realization. The figure of merit calculation indicates that our PRC can outperform recently reported daytime PRCs.