Study On The Relative Reflectance Of Silicon By Femtosecond Laser Texturing

Nowadays,energy crisis and environmental pollution have become a serious problem.The development of new sources of energy is more and more important to today's world.solar energy may be treated as a renewable,inexhaustible and clean energy sources.However,to date,the energy conversion efficiency of silicon-based solar cell is relatively low.To obtain silicon-based solar cells with higher energy conversion efficiency,it is very important to reduce the surface reflection of solar cell.In general,surface texturing is the most common and effective technique used to enhance the efficiency of light trapping on silicon surface,which can significantly reduce the optical reflection of the samples.In this paper,we fabricate the surface microstructures for reducing the relative reflectance of the silicon surface via femtosecond laser.The contents of this paper are divided into the two parts:(1)Using a direct femtosecond laser surface texturing technique,the textured surfaces with triangles,perpendicular grooves,hexagons and parallel grooves were fabricated on the surface of the monocrystalline silicon and multicrystalline silicon wafers,respectively.And the relationship between the relative reflectance and the microstructure shapes with the same period was also studied.The experimental results indicated that the shape of microstructure was very clear and neat.The treated surface with triangles microstructure can greatly decrease the reflection of the incident light,and their relative reflectances are less than 20%and 15%in the wavelength range from 400 to 1000 nm on the monocrystalline silicon and multicrystalline silicon surface,respectively.Furthermore,the effect of microstructures period on the relative reflectance of treated surface was investigated as well.When the shape of microstructures was fixed,the relative reflectance of samples increased with increasing the period of microstructures,(2)we experimentally investigated the relationship between the relative reflectance of samples and the quasi uniform cone-like-array microstructures on the monocrystalline silicon.Firstly,through altering the laser focusing depth,we achieved parallel microgrooves with the scanning interval of 20?m on the monocrystalline silicon by femtosecond laser.When the laser focusing depth is 20?m,some of cone-like-array microstructures appear on the treated areas.And then we fabricated perpendicular microgrooves with the scanning interval of 20?m under the same experimental condition.When the laser focusing depth is 20?m,we achieve a large area quasi uniform cone-like-array microstructures on the treated areas.From the optical microscope images of treated ares,the average height of spike microstructures increases at first and then decreases with the increase of the laser focusing depth.When the laser focusing depth is 20?m,the color of the treated areas is the darkest,and the average height of spikes is also the highest.Meanwhile,through drawing the dependence of the relative reflectance of samples on the laser focusing depth,we find the experimental results are in agreement with the theoretical research.Namely,when the laser focusing depth is 20?m,the relative reflectance of the treated areas is the lowest.And the relative reflectances of the samples are as low as 15%and 9%in the wavelength range from 400 to 1000 nm for parallel grooves and perpendicular grooves,respectively.These results obtained in this work can provide a useful guide for further decreasing the reflectance of silicon.