Preparation And Characterization Of A-Si/c-Si Heterojunction Solar Cells

With the economy development of society,the problems of energy crisis and environmental pollution arise gradually.Looking for clean,renewable alternative energy has become a worldwide problem.In all kinds of clean energy,the development of photovoltaic industry is particularly rapid,and researching solar cells has become the most important aspect to promote the development of photovoltaic industry.At present,the mainstream technology of solar cells is still crystal silicon solar cells,but the emergence of new structure,new materials has injected vigor to the photovoltaic industry,and a-Si/c-Si heterojunction solar cell is a typical new structure of solar cells.a-Si/c-Si heterojunction solar cells have many advantages,including high efficiency,low cost,good stability and low preparation temperature.At present,the efficiency of heterojunction batteries is up to 26.7%,which was prepared by Kaneka Company of Japan.In addition,it has been commercially well utilized.In 2016,the efficiency of the modules reached 23.8%,a new record.In this paper,based on the special structure of a-Si/c-Si heterojunction solar cells,we prepared a-Si thin films with different thichness by magnetron sputtering on p-Si(100)monocrystalline silicon.Then we achieved the preparation of the emission layer with rapid thermal treatment technology to complete p-n junction,and explored the effect of different thichness of a-Si and diffusion conditions on the crystallinity of a-Si film and thickness of the emissive layer.At last,we characterized the performance of the a-Si/c-Si heterojunction solar cells.After the step profiler,scanning electron microscope,Raman spectroscopy test,X-ray diffraction and the current-voltage characteristic test,we finally reached the following conclusions:(1)The i-a-Si layer was prepared by magnetron sputtering using high purity intrinsic silicon target at 200 W RF power and 300? substrate temperature.Its resistivity reaches 1.27*105 ?·cm,which is within the reasonable resistivity range of intrinsic silicon.Besides,the a-Si film will not crystallize at this substrate temperature,and the average sputtering rate is about 292.05 nm/h.Scanning electron microscopy(SEM)showed that the surface morphology of the i-a-Si films was good.In addition,we finded that the thickness of the a-Si films decreased after etching and cleaning.(2)The depth of p-n junction was measured by the lapping and staining method.The results showed that increasing diffusion temperature or prolonging diffusion time could increase the depth of diffusion.The calculated diffusion rates at 700?,750?,800? and 850? are about 14 nm/s,14.2 nm/s,14.5 nm/s and 19.8 nm/s,respectively.Therefore;we can adjust the depth of p-n junction according to the trend of the above junction depth,in order to obtain p-n junction with better quality.(3)We systematically studied the effect of diffusion temperature and diffusion time on the crystallization of a-Si films.Raman spectroscopy and X-ray diffraction were used to characterize the films,and the results of them are the same.The a-Si films with different thicknesses have different initial crystallized conditions after rapid thermal diffusion.The thicker the a-Si film is,the more preferential the crystallization will begin.It proves that there is a crystallization gradient between the bottom and the surface of microcrystalline silicon film,that is,the crystallization rate at the bottom is low,but the crystallization rate at the surface is high.Therefore,in view of the crystallization of a-Si films,the choices of rapid thermal diffusion are below 850 ??10 s or 800 ??60 s,850 ??50 s,850 ??70 s,900??70 s,900??70 s,whose thickness of a-Si films are 1135 nm,847 nm,553 nm,448 nm and 319 nm respectively.(4)We fabricated a-Si/c-Si heterojunction solar cell prototype device and tested its current-voltage characteristics.Through analysis,we can conclud that the best efficiency of a-Si/c-Si heterojunction solar cell is 8.25%,which was prepared at the diffusion condition of 800??20 s,and has a-Si film with thickness of 319 nm.In addition,the ISC,VOC,and F.F.are 24.412 mA,451.750 mV,0.482,respectively.