Controllable Preparation And Structure-activity Analysis Of High-entropy Alloy-based Solar Selective Absorption Coatings

Based on the characteristics of multi-principal in high-entropy alloys such as multi-principal design enhances interband transition and excellent thermal stability at high-temperature conditions.Controllable preparation and structure-activity analysis of high entropy alloy-based solar selective absorption coatings is researched in this paper.The solar selective absorption coatings（SSAC）which use AlTaTiZr,CuCrMnCoAl,and NbTaTiV based nitride as the absorption layer are prepared by magnetron sputtering technology at N₂ atmosphere,respectively.Excellent spectrally selective and high-temperature thermal stability of coatings is expected,which is used to enrich solar selective absorption coatings kinds and explore the application potential of high entropy alloy for solar absorption.The different solar selective absorption coatings were researched from the perspective of optical simulation,controllable preparation,structure-activity analysis,and performance evaluation,and discussed application fields according to the performance.The detailed research is as follows:1.For research the application potential of AlTaTiZr high entropy alloy on solar energy harvesting,the solar selective absorption coating with a single absorption layer of AlTaTiZr N is designed.The absorbing ability further increasing by the destructive interference when the Si₃N₄ layer as the antireflection layer deposited on the AlTaTiZr N layer.After optimization parameters,the absorptance of coating reaches 92.7%and low thermal emittance of 8.4%,showing an outstanding spectral selectivity.The enhancement of solar absorption by the Si₃N₄layer as an antireflective layer was elucidated by simulations with Finite Difference Time Domain（FDTD）software.The density functional theory（DFT）calculations demonstrate that the outstanding solar energy harvesting results from the enhanced d-d interband transition due to the multi-principal design.The vacuum thermal stability of coating was researched by short-term and long-term annealed treatment,and the failure mechanism of the coating was discussed by X-ray diffraction（XRD）,Raman spectra,and scanning electron microscope（SEM）.Upon vacuum heat treatment at 750°C for 120 h,absorption properties remain at a high level(α=0.933,ε_82°C=0.094).Coating shows a high equilibrium temperature of 95.3°C under 1 k W·m^-2 illumination.Outstanding photothermal conversion and thermal stability contribute to the application of the vacuum collector tube.2.The results of previous studies have shown that the absorption ability of coating will further increase with a reasonable design in the optical constants of the double absorption layer.In this work,a solar selective absorption coating with CuCrMnCoAl N double absorption layer was prepared.Compared with the single absorption layer coating,the absorptance of the double absorption layer increased to 95.2%due to the promotion of absorption in the UV region.The equilibrium temperatures of the coating under air and vacuum conditions were obtained by COMSOL simulation.According to the simulation results,the thermal stability of coating under different conditions was conducted.Thermal stability test results demonstrate that the coating meets the demand of operating under different environments.The coating shows a high equilibrium temperature of 110°C under 1 k W·m^-2 illumination,and is suitable to drive thermoelectric generators to realize photoelectric conversion.3.An infrared reflectance layer between the substrate and absorption layer was used to maintain spectral selectivity when the coating was deposited on the different substrates.In this chapter,a solar selective absorption coating with NbTaTiVN double absorption layer was prepared,the Al layer as the infrared reflectance layer was introduced and optimized the sputtering parameters of the other layers.The coating shows excellent spectral selectivity and effectively improves the photothermal conversion ability when the coating with a four-layer is deposited on the PVA substrate.The deposition of the Al layer reduces the additional heat loss caused by infrared thermal emission and improves the equilibrium temperature,contributing to its application in the direction of water evaporation.Subsequently,the coating deposited on other substrates under the same sputtering parameters shows excellent spectral selectivity, which proved the good universality of this four-layer structure.