Research On Black Silicon Thin-film Prepared By Chemical Etching And Optical Properties

By comparing the current researches on the preparation of the light trappingstructure on the silicon surface home and abroad, we found that black silicon is anew material with high solar absorption rate, black silicon achieve good sunlightabsorption effect in a wide range of wavelength, we call it good broad-spectrumabsorption property, so it has very important applications in the photovoltaic sectoraera.Black silicon is prepared by chemical etching method, study the influence ofmorphology to the absorption rate of black silicon and etching mechanism, lighttrapping mechanism as well as precious metal catalytic mechanism. The reflectivityof black silicon, surface morphology, surface composition, section structure,electrical parameters and other properties of the silicon wafer with AFM, SEM, XRF,UV-visible absorption （transmission） spectrometer, semiconductor parametric testerand other testing tools.The results indicate: with HAuCl₄as the catalyst, H₂O2as the oxidant, HF as thecomplexing agent, H₂O as the release agent, the process parameters of ultrasonicassisted etching of monocrystalline silicon is finally known.By observing the surfacemorphology of black silicon in different parameters （ultrasonic, etching time andtemperature）, we study the influence of porous structure to the absorption rate ofblack silicon. The results shows that when the height to diameter ratio of the porousstructure is0.6, the highest absorption rate reaches98.874%, which shows a goodperformance in the visible region in300-800nm that the reflectivity reduced to1%.The etching mechanism in the process is also analyzed, the etching reaction isprocess under and around the gold nanoparticles which as the active point, H₂SiF6and H₂is generated, thus the removal of the surface of the silicon forms porousstructure which increase the secondary reflective to improve the solar absorption.The electrical properties also showed excellent performance which the conversionefficiency reaches15.18%. The catalysts were optimized under the premise of costsavings, using AgNO₃instead of HAuCl₄, etching monocrystalline silicon twice tobuild porous–pyramid structure by using KOH/IPA as the etching solution, Theformation of porous structure on the pyramid makes the black silicon moreresponsive to short-wave light. The solar absorptance of black silicon is97.956%andthe conversion efficiency is13.34%. Both systems have a substantial increase in the solar absorption rate and conversion efficiency of monocrystalline silicon.