Theoretical Analysis Of Parameter Optimization For Antireflection Structure Of Photovoltaic Cell

In order to protect the fragile photovoltaic (PV) cell materials, optical protective coatingwas normally added on the surface of the PV cell. However, it will reflect part of the incidentlight, and then reduces the photo-electric-conversion efficiency greatly. Therefore, measuresshould be taken to reduce the loss of the light. At present, one technical processing to achieveantireflection is to etch gratings at the protective coating on the surface of the PV cell. Based onequivalent medium theory and optical thin film theory, we derived the reflectivity of etchinggrating structure. Using numerical simulation and theoretical analysis, we studied the impacts ofstructural parameters of grating on reflectivity. And we got the parameters in achievingantireflection for a wide spectral range and large-angle range of incident light. Our achievingacademic results are as follows:1. Based on equivalent medium theory and Fresnel formula, also the refractive indexformula of sub-wavelength grating which derived from the electromagnetic theory, we got theexpression of reflectivity of the grating, as well as expressions of several key parametersaffecting the reflectivity. This provided ways to decrease reflectivity of the grating.2. The key parameters of antireflection gratings are phase, etching depth and duty ratio, etc.Where, phase was mainly determined by etching depth and duty ratio. Etching depth wasdetermined by wavelength of incident light while duty ratio was determined by incident mediumand substrate material. The expressions of several key parameters showed that etching depth wasproportional to the wavelength. Namely, in order to guarantee each light in the range of visiblelight to have minimum reflectivity, the surface of grating should be bevel instand of planar, and the slope of bevel is0.61.3. The values of structural parameters showed that different polarized light had differentduty factors. It was similar to a two-dimensional grating effectively. This indicated that in viewof antireflection the morphology of two-dimensional sub-wavelength grating is more reasonable.