Simulation And Experimental Research Of Photonic Crystal Emitters And Filters For Silicon-based STPV Applications

Efficient use of solar energy has always been the goal of people's diligence,especially for China.Among the many ways to use solar energy,solar thermophotovoltaic systems have attracted great attention because of their potential for efficient use.The core of STPV is to efficiently regulate the solar spectrum,and designing a selective emitter and a filter of appropriate wavelength for the bottom battery is one of the keys to improving system performance.In this paper,the spectral modulation properties of two-dimensional silicon-based photonic crystals and silicon-based F-P cavity filters are studied and discussed.The main contents and results are as follows:1.From the perspective of coupling mode theory,the regulatory effect of two-dimensional photonic crystals on the spectrum is discussed.The emission characteristics of two-dimensional tungsten photonic crystals with cylindrical hole array are discussed by using FDTD Solution software to simulate the emission spectrum of different structures.The influence of cylindrical hole structure parameters on the emission characteristics of two-dimensional tungsten photon crystals is obtained:the radius of cylindrical hole is positively correlated with the cut-off wavelength,the deeper the cylindrical hole and the smaller the cycle,the higher the average emission rate of the high emission part of the emission spectrum.Based on the conclusions drawn from two-dimensional tungsten photon crystals,we designed a silicon-based photon crystal selective emitter coated with tungsten.The structure is a cylindrical hole array carved on the silicon substrate and a metal layer of tungsten coating with a certain thickness is added to the inner wall of the hole.It has excellent selective emission characteristics in simulation,and can well combine advanced silicon-based microelectronic processing technology,which is expected to be widely used in silicon-based thermal photovoltaic systems.At a temperature of 1458 K,the radiation spectrum simulated by the above-mentioned silicon-based photonic crystals has a high energy density in the wavelength range of 1.5 to 2.1?m,and a low energy density in the range of less than 1.5?m and greater than 2.1?m.2.From the perspective of interference theory,the working mechanism of multi-layer F-P cavity filter is discussed.By using FDTD Solution software,the transmission spectrum of the structure is simulated,and the influence of the number of layers and alternating order of DBR composed of different refractive index materials on the transmission spectrum is discussed.The simulation results reveal that the more cycles the DBR has,the smaller the half-width full height of the transmission peak,and the lower the average transmission rate of the cut-off area on both sides of the transmission peak.However,these changes become weaker and weaker as the number of cycles increases further.In addition,we also found that the outermost layer of high refractive index materials can make the DBR layer reflector higher,compared to the outermost layer of a lower refractive index material structure,such a structure can not only obtain a higher quality factor transmission peak,but also reduce the impact of material absorption.By balancing process difficulty and performance improvements,we eventually chose a microcavity with 2.5 DBR cycles.By changing the thickness of the microcavity,the transmissible transmission peak wavelength is achieved,with a well-performing transmission peak at 1.1?m,1.5?m,and 2.0?m,respectively.3.a-SiN_x/a-SiN_yO_z microcavity structure was prepared in PECVD system.Firstly,the refractive index and element composition of the a-SiN_x/a-SiN_yO_z material obtained by different experimental parameters are discussed,and the refractive index of a-SiN_0.4 and a-SiN_0.5O_1.7 are selected as two materials for the microcavity.The mode selection of a-SiN_0.5O_1.7 luminescent spectrum was realized by using microcavity structure,which confirmed the regulatory effect of the structure.In turn,a filter with a central wavelength of 1.1?m and 2?m was designed for the application of STPV system.In the experiment,the transmission peak at the wavelength of 1.11?m was obtained,with a peak of 81%and a half-width full height of 76 nm,as well as a transmission peak at the wavelength of 1.98?m,with a peak of 77%and a half-width full height of 130 nm.The transmission spectrum obtained by the simulation and experiment is well matched,but not exactly coincides.Finally,we analyze the causes of this difference from the extinction coefficient of the material,the interface roughness between the membrane layers,the deviation of the refractive index of the material and the various errors in the experiment.