Research On Optical Properties Of Silicon Solar Cells And Modules

Solar cells are photoelectric devices that converts optical energy into electrical energy.Improving the optical and electrical performance of solar cells is the main goal of research.This dissertation focuses on the optimization and characterization of optical performance of silicon solar cells and modules.First,the optical performance of solar cells and modules is optimized to reduce the loss of optical energy.This dissertation mainly discusses the pyramidal texture structure on the silicon surface,silicon nitride anti-reflection film,packaging materials of solar modules and its surface anti-reflection method.Then,a solution is proposed to the rapid detection of the optical performance of large-area silicon solar cells and modules.This novel method can solve the time-consuming problem when we characterize the reflectivity of large-area silicon samples.In this dissertation,we first establishes a mathematical analysis model on the optical path of the silicon surface texture,and reveal that there are up to seven light paths in the pyramidal structures,including a ray path with two reflections,three ray paths with three reflections,two ray paths with four reflections and a ray path with five reflections.The reflectivity of each ray path is mainly determined by the number of reflections.The more reflection times,the lower the reflectivity of the ray path.At the same time,the incident angle and the polarization direction of ray also affect the reflectivity.The larger incident angle causes,the higher reflectivity.The closer the incident angle is to the Brewster angle,the lower the reflectivity of p-polarized light.Through the analysis of the proportion of the seven kinds of ray paths in each structure,it is concluded that the optical performances of the random inverted pyramid structure and the regular inverted pyramid structure are almost same,which is superior to the random upright pyramid structure.The regular upright pyramid structure has the worst optical performance.In order to further analyze the optical performance of the random inverted pyramid structure,an overlapping inverted pyramid structure model was proposed and analyzed in detail.Finally,based on analysis results of the overlapping inverted pyramid structure,a new chain inverted pyramid structure is proposed.The analysis results show that the chain inverted pyramid structure has more excellent optical performance in that the proportion of the fourth reflection path is as high as10.33%.Experimentally,a chain inverted pyramid structure was successfully prepared on the diamond wire sawing silicon wafer through copper metal catalytic etching method.The results show that the reflectivity of the chain inverted pyramid structure smaller than that of random inverted pyramid structure.For silicon solar modules,there are five main optical losses.Based on the seven ray paths and the ray path of one reflection,the optical loss of each part of the module is analyzed.The analytical results show that the interface between the glass and air has4%optical loss in all optical paths.For the two reflection ray paths,the optical loss that escapes again from the surface of the solar cell reaches 1.15%.Therefore,in order to improve the optical performance of silicon solar modules,a systematic optimized analysis was conducted on materials of each layer in silicon solar cells and modules.The optimized analysis of the Si₃N_x anti-reflection film under the consideration of the packaging material shows that the refractive index of Si₃N_x should be adjusted from 2.0to 2.4 compared with the optical optimized result of only considering the solar cell.The thickness of Si₃N_x film also needs to be adjusted accordingly.The analytical results of the packaging materials show that any refractive index of the packaging material will result in the power loss of the modules.The packaging loss increases with the increase of the refractive index of the packaging material.In order to reduce the optical loss at the interface between the encapsulating glass and the air,the optical properties of the coated glass,patterned glass and coated patterned glass were analyzed systematically.The analysis results showed that the coated glass with a coating of n=1.2 and t=120nm,the vertical transmittance increases from 96%of the flat glass to 99.25%,and the omnidirectional transmittance increased from 93.26%of the flat glass to 97.22%.However,when the incident angle is larger than 60°,the transmittance of coated glass drops as fast as that of flat glass.The vertical transmittance of patterned glass increases rapidly when the tilt angle?is larger than 30°.When the tilt angle?is larger than 45°,the increase of vertical transmittance gradually slows down.The omnidirectional transmittance of patterned glass increases with the increase of the tilt angle?.When?is larger than 30°,the patterned glass has a good transmittance at an incident angle of0°to 90°,therefore the omnidirectional transmittance of the patterned glass gradually increases.In order to obtain the best optical performance,the application of coated patterned glass is suggested.The analytical results show that the patterned glass with a coating has both antireflection advantages of coated glass and patterned glass.When the coating layer is used with n=1.2,t=120 nm,and the tilt angle of the patterned structure?is 30°,the vertical transmittance of the coated patterned glass reaches 99.15%and the omnidirectional transmittance reaches 99.17%.Finally,a solution to the problem of rapid detection of the optical performance of large-area silicon solar cells and modules is proposed in this dissertation.A novel type of reflectivity test method is put forward based on the changing of the resolution of the CCD photodetector from the conventional resolution of the wavelength to the resolution of the sample in the spatial position,resulting in the rapid measurement of the reflectance of each point on the sample.According to the testing principle,the spectrum L???of the light source needs to be proportional to the quotient of the AM1.5standard sunlight spectrum G???and the photodetector response Q???.By introducing the correction factor,the light source spectrum requirements can be appropriately reduced.A prototype instrument was designed and fabricated.Through the testing of monocrystalline silicon textured wafer,it is verified that the new reflectivity measuring instrument has the similar accuracy as the UV-VIS spectrometer,which is obviously better than the commercial D8 integral reflectivity testing instrument.At the same time,the repeatability error of the new reflectivity measuring instrument is only 0.1%,which is much lower than the repeatability error of>1%of the D8 integral reflectivity testing instrument.In addition,the instrument has the advantages in large area testing,high test area resolution,and fast test speed.Therefore,the new instrument is expected to be used for online reflectance measurement and appearance judgment in the production process of silicon solar cells and modules,which is helpful to improve the yield and reduce the costs.