The Fabrication And Optimization Of Nanowires Black Silicon Solar Cells Based On Chemical Etching

In the 21 st century,coal,oil,natural gas and other conventional energy will face the depletion in 2050.And solar energy as an inexhaustible,clean energy is more widely used.According to different materials used,the solar cells may further be divided into: monocrystalline silicon solar cells,polycrystalline silicon solar cells,organic solar cells,polyhydric compound thin film solar cells,heterojunction tandem solar cells,etc.,in which the monocrystalline silicon solar cells have been first studied.Now it is also the fastest growing and the most mature,which has occupied a major position in practical applications.There are two main factors on the restriction of photoelectric conversion efficiency of silicon solar cells: 1.The loss of the incident light which dues to the high surface reflectance;2.The photo-generated carriers cannot be effectively collected which caused by the interior and surface recombination of the solar cells.In order to improve the conversion efficiency of silicon solar cells,we studied from two ways which are the reduction of surface reflectance and the suppression of photo-generated carriers:(1)Using the metal-assisted chemical etching method to fabricate nanowires structure whose feature size is nanometer,in order to reduce the surface reflectance.First,we systematic did the experience of fabricating nanowires structure by metal-assisted chemical etching,analyzed the reaction mechanism,influence factors,production transportation and the other etching characteristics,then we characterized the properties of black silicon by surface reflectance testing,scanning electron microscope obverse and the other methods;after this,we combined the nanowires structure and the traditional pyramid structure to fabricate the micro/nanometers multi-scale black silicon.The result showed that this structure could reduce the surface reflectance below 5%.(2)Adopting the tetramethylammonium hydroxide solution to etch the black silicon surface after phosphorus diffusion,in order to suppress the recombination of photo-generated carriers.First,we systematic analyzed the anisotropic etching characteristics on silicon surface of tetramethylammonium hydroxide solution,then we used the tetramethylammonium hydroxide solution to etch the black silicon after the phosphorus diffusion,aimed to reducing the thickness of “dead layer” which caused by the process of thermal diffusion,after that we characterized the surface morphology change and the minority carriers lifetime,the result showed that the minority carriers lifetime increased greatly after the chemical etching,which means the recombination of photo-generated carriers have been suppressed effectively.Finally,we optimized the fabrication technology of black silicon solar cells such as: the time of tetramethylammonium hydroxide etching,the kind of surface passivation layer and so on.Then we actually fabricated the black silicon solar cells by using the optimized technologies,and made testing and analysis on minority carrier lifetime,surface reflectance,I-V characteristics and quantum efficiency.The results proved that: both the surface recombination and Auger recombination could be suppressed at the same time by tetramethylammonium hydroxide solution etching after thermal diffuion.So that the open-circuit voltage,short-circuit current and quantum efficiency of black silicon solar cells are all improved greatly.Finally,the photoelectric conversion efficiency rose from 12.2% to 15.5%,is higher than that of traditional alkaline texturing of solar cells(15.3%)which was fabricated at the same batch.