Study On Periodic Nanostructures For Thin Film Silicon Solar Cells

Since the absorption coefficients at wavelengths near bandgap and the thickness of the thin-film silicon absorption layer is less than the intrinsic absorption length at most of the solar wavelengths,its absorption efficiency is very low,which greatly limits the application of the thin-film silicon solar cell.The addition of the light trapping structures can reduce the surface reflectivity and increase the light path in the absorber layer,thus improving the absorption efficiency of the thin film solar cell.In this dissertation,based on the analysis of existing trapped structures,two new types of periodic light trapping structures are proposed:periodic inverted prism structure and Fourier-series based on periodic nanostructure(FSPN).The theoretical and experimental study of these two structural properties has been carried out.The main contents are as follows:First of all,a periodic inverted inverted prism structure with better performance was proposed and optimized.When the thickness of the absorber layer is 2?m,the textured cell has a short circuit current density of 33.1mA/cm~2,62.3%higher than that in flat solar cell and 11.4%higher than that optimal inverted pyramid textured solar cell.In terms of angular response,for periodic inverted prism structure,there is no decrease within 60°.The short-circuit current density remains 21.7mA/cm~2 at an incident angle of 80°.Then,in order to further improve the angle insensitivity,Fourier-series based on periodic nanostructure(FSPN)was proposed.The optimal 1-D and 2-D FSPN structures were found through global optimization.For 1-D FSPN structure,the solar cell achieves a short-circuit current density of 24.7mA/cm~2 with the silicon thickness of only 1?m.For 2-D FSPN structure,the short-circuit current density increase up to 27.1mA/cm~2,it has better performance than optimal inverted pyramid textured and cosine structure,and it also has excellent full-angle light absorption enhancement.Finally,a periodic inverted prism structure was fabricated by using the combination of interference lithography and wet etching.Trigonometric periodical hole arrays were fabricated on the photoresist using interference lithography,followed by wet etching to transfer the array nto the silicon wafers.Optimal inverted prism structures were produced.The average reflectance can reach 7.8%,76.5%lower than that of the flat silicon film,which is superior to the inverted pyramid structure.