A near-ideal solar selective absorber with strong broadband optical absorption from UV to NIR

Near-perfect spectrally-selective metasurface solar absorber based on tungsten octagonal prism array

Solar selective absorbers influence the photothermal efficiency of high-temperature solar thermal applications directly and significantly. In present work, a metasurface absorber consisting of an octagonal prism array is proposed, optimized and analyzed. Firstly, the structure parameters of the absorber are optimized, finding the optimal absorber achieves near-perfect spectrally-selectivity compared with the perfect solar absorber. The high solar absorptivity of 0.9591, low emissivity of 0.1594-0.3694, and high photothermal efficiency of 94.72-83.10% are achieved at 1073-1573 K and 1000 suns. Then, the mechanisms leading to the excellent spectral selectivity are investigated, suggesting that the coupling effects of multi-plasmon resonance modes and the impedance matching lead to the high solar absorptivity. Meanwhile, the impedance mismatching is the mechanism to minimize the emissivity in the mid-IR region. Moreover, whether the spectral absorptivity can be changed by structural parameters is investigated, suggesting that the excircle diameter of the first tungsten octagonal prism and the height of SiO2 under the octagonal prism can influence the spectral absorptivity obviously. Finally, the metasurface absorber is demonstrated to be highly insensitive to both polarization and incident angles. These results suggest that the proposed metasurface absorber should be suitable for high-temperature solar thermal devices.

Nanostructured multilayer hyperbolic metamaterials for high efficiency and selective solar absorption

Highly efficient solar-to-thermal conversion is desired for the renewable energy technologies, such as solar thermo-photovoltaics and solar thermo-electric systems. In order to maximize the energy conversion efficiency, solar-selective absorbers are essential with its absorption characteristics specially tailored for solar applications. Here, we propose a wideband spectral-selective absorber based on three-dimensional (3D) nanostructured hyperbolic metamaterial (HMM), which can realize near-unity absorption across the UV and NIR spectral ranges. Moreover, the optical topological transition (OTT) of iso-frequency surface (IFS) is manipulated to selectively enhance light absorption in the entire solar spectrum, crucial for improved energy utilization. Impressive solar-to-thermal conversion efficiency of 95.5% has been achieved. Particularly, such superior properties can be retained well even over a wide range of incident angles. These findings open new avenues for designing high-performance solar thermal devices, especially in the fields related to solar energy harvesting.

A flower-inspired divergent light-trapping structure with quasi-spherical symmetry towards a high-performance flexible photodetector

Molybdenum disulfide (MoS2) has received widespread attention in recent years due to its exciting properties. However, the practical applications of MoS2 in optoelectronic devices are impeded by the power supply problem, the lack of flexibility, and the low light absorption for planar nanosheets and nanosheet arrays. Inspired by the elaborate architecture of the flower Tagetes erecta L., in this work, a self-assembled divergent MoS2 nanoflower (MoS2_F) with quasi-spherical symmetry is successfully synthesized by a facile one-step hydrothermal method. It is of significance that coupled with asymmetric silver electrodes and packaged by polymethyl methacrylate (PMMA), a self-powered flexible photodetector (PD) based on MoS2_F is actualized and shows an excellent flexible photoresponse performance at zero bias voltage. The divergent structure with quasi-spherical symmetry enables the MoS2_F to achieve strong broadband and omnidirectional absorption (92.7%) and ensures that the MoS2_F maintains the same physical contact on a different bending degree. Intriguingly, excellent flexibility and stability have been achieved as MoS2_F PD retains 91.4% of the initial efficiency even when bent to 151° and retains 92.5% of the initial efficiency even after 1000 bending cycles. Therefore, by a low-cost process, this work demonstrates an innovative avenue to fabricate a self-powered flexible photodetector with excellent light absorption, broadband response, flexibility, and stability, which is of great practical significance for optoelectronic applications in various environments.