Lithography-free wide-angle polarization-independent ultra-broadband absorber based on anti-reflection effect

Angle-Insensitive Ultrathin Broadband Visible Absorber Based on Dielectric-Semiconductor-Lossy Metal Film Stacks

Ultrathin broadband absorbers with high efficiency, wide angular tolerance, and low fabrication cost are in demand for various applications. Here, we present an angle-insensitive ultrathin (<150 nm) broadband absorber with an average 96.88% (experiment) absorptivity in the whole visible range by utilizing a simple dielectric-semiconductor-lossy metal triple-layer film structure. The excellent broadband absorption performance of the device results from the combined action of the enhanced absorptions in the semiconductor and lossy metal layers exploiting strong interference effects and can be maintained over a wide viewing angle up to ±60°. Benefiting from the lossy metal providing additional absorption, our design reduces the requirement for the semiconductor's material dispersion and has great flexibility in the material selection of the metal layer. Additionally, the lithography-free nature of the proposed broadband visible absorber provides a high-throughput fabrication convenience, thus holding great potential for its large-area applications in various fields.

All-day uninterrupted thermoelectric generator by simultaneous harvesting of solar heating and radiative cooling

Passive power generation has recently stimulated interest in thermoelectric generators (TEGs) using the radiative cooling mechanism. However, the limited and unstable temperature difference across the TEGs significantly degrades the output performance. In this study, an ultra-broadband solar absorber with a planar film structure is introduced as the hot side of the TEG to increase the temperature difference by utilizing solar heating. This device not only enhances the generation of electrical power but also realizes all-day uninterrupted electrical output due to the stable temperature difference between the cold and hot sides of the TEG. Outdoor experiments show the self-powered TEG obtains maximum temperature differences of 12.67 °C, 1.06 °C, and 5.08 °C during sunny daytime, clear nighttime, and cloudy daytime, respectively, and generates output voltages of 166.2 mV, 14.7 mV, and 95 mV, respectively. Simultaneously, the corresponding output powers of 879.25 mW/m², 3.85 mW/m², and 287.27 mW/m² are produced, achieving 24-hour uninterrupted passive power generation. These findings propose a novel strategy to combine solar heating and outer space cooling by a selective absorber/emitter to generate all-day continuous electricity for unsupervised small devices.

Plasmonic Nanostructures for Broadband Solar Absorption Based on Synergistic Effect of Multiple Absorption Mechanisms

The growing attention to solar energy has motivated the development of highly efficient solar absorbers. In this study, a high-performance meta-structure solar absorber (MSSA) based on a tungsten truncated cone structure combined with a film resonator structure has been proposed and demonstrated numerically. The designed structure exhibits over 97.1% total solar absorption efficiency and less than 8.5% total thermal emissivity under the condition of one solar concentration, hence reaching 91.6% photothermal conversion efficiency at 100 °C. In addition, the proposed MSSA achieves promisingly high spectrum absorptance of over 97.8% in the ultraviolet, visible and near-infrared regions (280-1700 nm). Based on the simulation analysis, the enhanced light absorption is attributed to the synergistic effect of the magnetic polaritons (MPs) on the nanostructured metal surface, the cavity plasmon resonance between the truncated cones that can form light-trapping structures, the magnetic field resonance of the metal-insulator-metal (MIM) optical resonator and the inherent loss of tungsten. The impedance of the absorber is well matched with free space. Furthermore, the optimized absorber shows great potential in solar thermophotovoltaic applications that require wide-angle polarization-independent ultra-broadband light response characteristics.