Design,Fabrication And Application Of Solar Selective Absorbers Based On Multilayered Structure

Solar photothermal conversion,a relatively mature solar energy utilization technology,is easy to collect solar energy with simple structure,high conversion efficiency and low cost.Moreover,the storage property of heat can greatly suppress the unfavorable effects of climate variation on solar energy utilization.Solar selective absorber plays an important role in the solar photothermal conversion system.Metal/dielectric multilayered solar selective absorbers have many advantages,such as good and stable spectral selectivity,high absorptivity and low thermal radiation rate,simple preparation technology,low cost,no pollution,corrosion resistance.With the demands for higher working temperature and longer temperature,middle and high-temperature solar selective absorbers have been the research hotspot in recent years.For metal/medium multilayered films,the key is to inhibit the degradation of the structure and properties under high temperature environment,so as to improve the working temperature and high-temperature tolerance time,as well as ensuring the service life of the films.In this dissertation,the design,preparation and application of metal/dielectric multilayered solar selective absorbers were studied,with emphasis on the thermal stability of the films.In initial,the design and simulation methods of solar selective absorbers were studied.The optical constants obtained by ellipsometry measurement and fitting were proposed as the modeling parameters of multilayer films.Secondly,the preparation processes and performance characterization methods of metal/medium multilayered films were showed in detail,as well as the calibration methods of deposition rate.Ellipsometry was proposed to calibrate the thin metal films with extremely thin film thickness,and corresponding sample-preparation and ellipsometry analysis methods were showed as well.In the research on thermal stability of solar selective absorbers,Cu?500 nm?/Al₂O₃?60 nm?/Cr?18nm?/Si O₂?66 nm?/Cr?4 nm?/Si O₂?83 nm?were designed and prepared.The Al₂O₃ barrier layer deposited by the atomic-layer-deposition is used to prevent the diffusion of the active Cu element in the reflective layer.The sample has a solar absorptivity of 95.4%and a low thermal emissivity of14.7%?773k?,showing an excellent spectral selectivity.After heat treatment at 500°C for 72 hours,the solar absorption rate decreased by about 3.3%and the thermal emissivity decreased by about4.4%,meeting the performance standards of solar selective absorbers for application in the range of medium and high temperature.Compared with the multilayered film structure with similar film thickness prepared by magnetron sputtering method,it is fully proved that the accession of ALD-Al₂O₃ diffusion barrier layer with dense structure can significantly improve the thermal stability of the films.The solar selective absorbers proposed has an excellent thermal stability,high absorptivity and low thermal emissivity,which can be applied to various solar energy conversion systems at medium and high temperatures in the future,such as solar heating,solar energy collection and solar thermal power technology.Finaly,based on the high-performance solar selective absorbers obtained above,we designed and fabricated a solar-thermo-electric device,which can convert sunlight energy to electric directly.The platinum electrodes were deposited on thermoelectric couples on one side of the glass substrate,while solar selective absorber with the film structure of Cu?350 nm?/Si O₂?14 nm?/Cr?19 nm?/Si O₂?49nm?/Cr?6 nm?/Si O₂?62 nm?is deposited on the other side of the substrate.To enhance the adhesion between the multilayered film structure and the glass substrate,the Cr thin film with thickness about10 nm was added.The device has negligible response when it was not illuminated by light,while the voltage and current were generated rapidly under the illumination.This achievement broadens the application of solar photothermal conversion thin film and thermoelectric thin film,showing a broad prospect in the fields of solar power generation and photoelectric detection in the future.