Theoretical Analysis Of Antireflection Structure Of Photovoltaic Cell Based On The Solar Spectrum

This work is mainly about theoretical derivation and numerical simulations of some structural parameters and shapes of sub-wavelength grating for antireflection structures of photovoltaic cells. The study includes the analysis of antireflection of one-dimensional single-step grating, multi-level rectangular grating and one-dimensional spectrum-based grating and two-dimensional grating. The main contents and main results are as follows:1. Based on the expressions of reflectivity of the grating and the expressions of parameters that determined the minimum reflectivity of grating, such as the duty ratio, etching depth and equivalent refractive index we got optimal parameter combinations, the refractive index of the substrate material is1.30, the duty ratio is0.46, the etching depth is150nm, of average antireflection of one-dimensional single-level rectangular sub-wavelength grating in the visible range using MATLAB simulation.We simulated the variation of reflectivity with wavelength of multi-level rectangular grating by recursive method. The results show that grating reflectivity volatility decreases with wavelength changes with the increase of etch layers, When the etch layers reaches a certain value, reflectivity fluctuations is no longer reduced, and tends to a fixed value gradually.In order to get better results, we continued to take actions on the etched parts. We got the refractive index of solar cell materials and the average reflectivity of etched parts in the visible range, as1.69and0.0055, respectively. Compared with the untreated cases, the reflectivity of the treated grating reduced by96.5%. Based on this, we proposed so called stepped bevel grating.2. From the approximation of equivalent refractive index of two-dimensional grating, we calculated reflectivity of two-dimensional grating. The results showed that, the mean effect of antireflection of two-dimensional grating is better than that of one-dimensional grating in the whole solar spectrum. However, it is opposite in the visible range. Namely the effect of antireflection of two-dimensional grating is prominent in the infrared region. When the duty ratios of two-dimensional square and rectangular gratings meet the conditions of f=[n0/(n0+nb)]1/2and fx×fy=no/(no+nb), respectively, the reflectivity remain the minimum.3. Using the blackbody radiation curve at6000K, we fit solar spectrum curve under AM1.5, which used as a weight and we got the evaluation function. On the basis of overall simulated annealing genetic algorithm of real number encoding, we obtained etch depth dj of each layer. The results showed that, the deeper the etch depth, the better the effect of antireflection, corresponding to the center wavelength of the solar spectrum. Due to the blackbody-radiation-curve-liked shape of grating, we called it spectral-shapedgrating.