Toward a Scalable and Cost-Conscious Structure in Spectrally Selective Absorbers: Using High-Entropy Nitride TiVCrAlZrN

Abstract

Enabling a highly enhanced optical performance and high-temperature thermal robustness, acting as a primary absorption layer material, remains a challenge in photothermal conversion systems, which is why the newly emerging high-entropy alloy (HEA) is introduced. Herein, we develop a high-entropy nitride TiVCrAlZrN-based spectrally selective absorber, providing the potential to strengthen structural and optical advancement through component selection and structure design. The combination of computer simulation and a magnetron sputtering method pioneers a double-layer structured coating with a sound solar absorptance (α = 92.4%) and an ultra-low thermal emittance (ε = 5.3%), leading to a high spectral selectivity (α/ε = 17.4). Investigating the structural and optical robustness demonstrates that the coating could endure heat-treatment at 800 °C for 2 h in a vacuum environment. At the same time, the research on long-term thermal stability indicates that the TiVCrAlZrN-based absorber could retain good optical properties after annealing at 550 °C for 168 h. Overall, the synergistic advantages of the convenient technology process, low-cost preparation, easily scalable production, and repeatability in this work promise potentially valuable applications for photothermal conversion techniques. The conceptual and practical breakthroughs promote practical applications of the HEA in photothermal fields and significantly extend the paradigm to devise a photothermal absorber.

Efficient Warming Textile Enhanced by a High‐Entropy Spectrally Selective Nanofilm with High Solar Absorption

“…For high‐entropy materials composed of transition metals, the d electron intensities around the Fermi level are enhanced compared with the low‐entropy counterparts; [ 33 ] besides, high‐entropy nitrides composed of transition metals have narrow bandgaps. [ 34 , 35 ] Therefore, d‐d transitions are easily activated, that is, the d‐band electrons with energy above the bandgap transit from the valence band to the conduction band, thereby enhancing solar harvesting capability in the UV–vis–NIR region. [ 36 ] Such d‐d band transition induced solar absorption is intrinsic and roughness‐insensitive.…”

High‐Entropy Photothermal Materials

“…[155] This absorber displayed impressive solar absorption (𝛼 = 92.8%) and low emittance (ɛ = 5.1%). Its entropy-driven stabilization effect countered diffusion and oxidation in the absorbing layer, maintaining high solar absorption even after annealing at 650 °C for 300 h. It is worth to note that the tri-layer spectrally selective absorbers with the same HE materials as dual absorption layers can only withstand thermal treatment at 600 °C for 10 h. [134] In subsequent works, various HE nitrides like quaternary MoTaTiCrN, TiVCrAlZrN, and AlCrMoTaTiN were explored as absorption layers, [156][157][158] all achieving solar absorptivity above 92% and enhanced thermal stability.…”