The objective of this study is to create a planar solar light absorber that exhibits exceptional absorption characteristics spanning from visible light to infrared across an ultra-wide spectral range. The eight layered structures of the absorber, from top to bottom, consisted of Al₂O₃, Ti, Al₂O₃, Ti, Al₂O₃, Ni, Al₂O₃, and Al. The COMSOL Multiphysics^® simulation software (version 6.0) was utilized to construct the absorber model and perform simulation analyses. The first significant finding of this study is that as compared to absorbers featuring seven-layered structures (excluding the top Al₂O₃ layer) or using TiO₂ or SiO₂ layers as substituted for Al₂O₃ layer, the presence of the top Al₂O₃ layer demonstrated superior anti-reflection properties. Another noteworthy finding was that the top Al₂O₃ layer provided better impedance matching compared to scenarios where it was absent or replaced with TiO₂ or SiO₂ layers, enhancing the absorber’s overall efficiency. Consequently, across the ultra-wideband spectrum spanning 350 to 1970 nm, the average absorptivity reached an impressive 96.76%. One significant novelty of this study was the utilization of various top-layer materials to assess the absorption and reflection spectra, along with the optical-impedance-matching properties of the designed absorber. Another notable contribution was the successful implementation of evaporation techniques for depositing and manufacturing this optimized absorber. A further innovation involved the use of transmission electron microscopy to observe the thickness of each deposition layer. Subsequently, the simulated and calculated absorption spectra of solar energy across the AM1.5 spectrum for both the designed and fabricated absorbers were compared, demonstrating a match between the measured and simulated results.

This study aimed to investigate a bidirectional switching functionality absorber, which exhibited an ultra-wideband characteristic in one direction, while in the other direction it demonstrated the absorption of three different resonant wavelengths (frequencies). The fully layered planar structure of the absorber consisted of Al₂O₃, Zr, yttria-stabilized zirconia (YSZ), Zr, YSZ, Al, YSZ, and Al. The simulations were conducted using the COMSOL Multiphysics^® simulation software (version 6.1) for analyses, and this study introduced three pivotal innovations. Firstly, there had been scarce exploration of YSZ and Zr as the materials for designing absorbers. The uses of YSZ and Zr in this context were a relatively uncharted territory, and our research endeavored to showcase their distinctive performance as absorber materials. Secondly, the development of a planar absorber with multifunctional characteristics was a rarity in the existing literature. This encompassed the integrations of an ultra-wideband optical absorber and the creation of a multi-wavelength resonant absorber featuring three resonant wavelengths. The design of such a multi-wavelength resonant absorber holds promise for diverse applications in optical detection and communication systems, presenting novel possibilities in related fields. Lastly, a notable discovery was demonstrated: a discernible redshift phenomenon in the wavelengths of the three resonant peaks when the thickness of YSZ, serving as the material of resonant absorber layer, was increased.

This study focused on designing an ultra-wideband metamaterial absorber, consisting of layers of Mn (manganese) and MoO₃ (molybdenum trioxide) arranged in a planar interleaving pattern, with a matrix square-shaped Ti (titanium) on the top MoO₃ layer. Key features of this research included the novel use of Mn and MoO₃ in a planar interleaving configuration for designing an ultra-wideband absorber, which was rarely explored in previous studies. MoO₃ thin film served as the fundamental material, leveraging its favorable optical properties and absorption capabilities in the infrared spectrum. Alternating layers of Mn and MoO₃ were adjusted in thickness and order to optimize absorptivity across desired wavelength ranges. Another feature is that the Mn and MoO₃ materials in the investigated absorber had a planar structure, which simplified the manufacturing of the absorber. Furthermore, the topmost layer of square-shaped Ti was strategically placed to enhance the absorber’s bandwidth and efficiency. When the investigated absorber lacked a Ti layer, its absorptivity and bandwidth significantly decreased. This structural design leveraged the optical properties of Mn, MoO₃, and Ti to significantly expand the absorption range across an ultra-wideband spectrum. When the Ti height was 280 nm, the investigated absorber exhibited a bandwidth with absorptivity greater than 0.9, spanning from the near-infrared (0.80 μm) to the mid-infrared (9.07 μm). The average absorptivity in this range was 0.950 with a maximum absorptivity of 0.989. Additionally, three absorption peaks were observed at 1010, 2510, and 6580 nm. This broad absorption capability makes it suitable for a variety of optical applications, ranging from near-infrared to mid-infrared wavelengths, including thermal imaging and optical sensing.

In this study, a simple pyramid-like ultra-wideband absorber was designed to explore high absorptivity across a wide bandwidth. The absorber consisted of eight layers organized into four groups, and each group comprised a metal layer followed by an oxide layer, both of which were square with equal side lengths. Specifically, the chosen oxides, arranged from bottom to top, included SiO₂ (t7 layer), Al₂O₃ (t5 layer), SiO₂ (t3 layer), and Al₂O₃ (t1 layer). In the initial design phase, the thickness of the t8 Ti layer was set to 50 nm and assigned initial values to the thicknesses of the t7-t1 layers, and the widths of the four groups w4, w3, w2, and w1, decreased successively from bottom to top, creating a structure reminiscent of a pyramid. Comsol (version 6.0) was utilized to simulate and systematically vary one parameter at a time, ranging from the thicknesses of the t7-t1 layers to the widths of w4-w1, in order to identify the most suitable structural parameters. Our analyses demonstrated that multimode resonance arose due to the emergence of absorption peaks at lower wavelengths between larger and smaller areas. Additionally, surface plasmon resonance and interference effects between various layers and materials were attributed to the alternating arrangement of metal and oxide layers. The enhancements in the electric field observed at different resonance peak wavelengths illustrated the Fabry–Perot cavity effect, while the impedance matching effect was observed through variations in the real and imaginary parts of the optical impedance with respect to the wave vector. After simulating using these optimally found thicknesses and widths, the aforementioned effects manifested in the pyramid-like ultra-wideband absorber we designed, with its absorptivity surpassing 0.900 across the spectrum from ultraviolet A (335 nm) to middle infrared (4865 nm).