Bioinspired Structured Metal‐Insulator‐Metal Metamaterials with Gradient Resonator for High Efficiency and Solar Selective Absorption

Efficient utilization of solar energy is crucial in addressing energy challenges. Solar selective absorption materials, like metal-insulator-metal (MIM) absorbers, are highly efficient in converting solar energy to heat due to their strong solar absorption and minimal radiation loss. However, traditional planar MIM absorbers have narrow solar absorption bands and limited spectral tuning, restricting their practical use. Inspired by marine diatoms, this study designs and fabricates a structured MIM metamaterial (SMM) to achieve omnidirectional and polarization-insensitive selective absorption. The SMM features a concave-structured design with gradient resonance cavities, significantly expanding absorption across the solar spectrum and enabling tailored electromagnetic responses for selective absorption in different wavelength bands. With a thickness of just 180 nm, the SMM absorber shows outstanding selective absorption, reaching up to 91% absorptivity in the 0.3-2.5 µm and emissivity only 0.09 in the infrared range. The SMM absorber also exhibits size insensitivity, reducing design constraints in practical applications. In terms of photothermal conversion, the SMM absorber demonstrates stable performance, achieving a surface temperature of 165 °C under 3 sun illumination. Compared to planar MIM structures, this structured design significantly enhances solar absorption without affecting infrared emissivity, offering a novel approach to improving selective absorption performance.