Solar Spectrum Selective Micro-nano Photonic Structure Characteristics And Preparation

In the new age of the low-carbon economic human society, more interests are focused on the solar energy as it is natural rich, clean and sustainable. The photo-thermal conversion can be the way to utilize the solar energy in high efficiency by matching the absorption spectra of the device to that of the solar radiation in wide spectral range, in which the photo-electric device only working in a limited spectral range has the drawback to compete. In this work, we have studied the optical properties of several micro/nano photonics structures with the design and fabrication to realize the devices for their potential applications in the future.1. We report a structure with 4 thin film layers composed of pure metal and dielectric materials which is prepared by RF-sputtering. The reflectance and transmittance are lower than 5% with the absorptance to be achieved higher than 95% in the 400-1000nm wavelength region matching with the solar radiance spectrum. The thermal emittance of the structure is in the range of 0.063-0.10 through data analysis. The good reproducibility and stability of spectral data associated with the deposition process imply the advantage of the solar energy absorber which is cost-effective with long-life reliability in application.2. The Fs laser-based two-photon polymerization (2PP) has been widely reported as a means of writing micro/nano structures. We have introduced axicon into the setup of traditional 2PP system to increase the structure writing speed. We studied the use of a large depth of focus Bessel beam in the fabrication of cell structures. Two axicon lenses were investigated for both the Bessel region's profile and the characteristics of the structures. High aspect ratio 3D micro/nano structures are fabricated to prove this method can get a high efficiency while maintaining high resolution.3. We invent a novel approach of making corrugated metal micro/nano structures by depositing metal onto the patterns, which are fabricated by 2PP. The reflection and transmission of these structures are measured and they show a good solar selective absorber's character. We found the absorption increases in a part of the spectrum, which can be related to the structure's dimensions. A RCWA code was used to define the optimal parameters for solar absorption in this system.