Research On Efficiency Enhancement Of Thin-film Solar Cells Based On Light Trapping Structure

Solar energy has become one of the most popular renewable energy sources due to its huge reserves and no secondary pollutants during use.Solar cells can absorb incident light energy and convert it into electricity,which is one of the important methods of using solar energy.Traditional crystalline silicon solar cells require hundreds of microns of ultra-high purity silicon wafers as raw materials,which will greatly increase the cost of power generation.In order to reduce the cost of power generation,thin-film solar cells with a thickness of only a few microns have gradually become the most popular research direction.Due to the sharp reduction of the thickness,it is unable to provide enough optical path for the long wavelengths incident light to be fully absorbed.Therefore,how to improve the absorption of thin-film solar cells has become the focus of researchers in this field.Previous studies have shown that designing nano structures can increase the light absorption rate of thin-film solar cells.The commonly used light trapping structures include nanoparticles,nano gratings,photonic crystals and antireflection coating.However,most of the current research results only have absorption enhancement effect in a narrower wavelengths,which can not achieve the full spectrum absorption enhancement of thin film solar cells.In this paper,in order to achieve the full spectrum absorption enhancement of thin-film solar cells,the finite-difference time-domain simulation method is used.Firstly,the influence of the position,material,size and distribution of nanoparticles on the absorption of solar cells is explored,and the location and materials of nano particles are optimized.Then,the influence of the number of layers,material and thickness of multilayer antireflection coating on the absorption of solar cells is studied,and the optimized structure of double antireflection coating is obtained.Finally,the mechanical tensile properties of the thin film solar cells are analyzed.In order to realize the full spectrum absorption enhancement of amorphous silicon thin film solar cells,two optimization schemes are proposed in this paper.One is to use a composite light trapping structure with Si O₂ nanospheres on the upper surface and Ag hemispheres on the substrate.This structure can improve the absorption of both long and short wavelengths simultaneously.Compared with the solar cells without light trapping structure,the short-circuit current density is increased by 21%,and the photoelectric conversion efficiency is increased by 18%.The second scheme is to use a double-layer antireflection coating and grating or hemisphere on the substrate to enhance the absorption of the full spectrum of thin-film solar cells.Compared with the solar cells without light trapping structure,this structure can improve the short-circuit current density by 39%and the conversion efficiency by 38%.The results show that the structure can maintain high absorption enhancement performance under the condition of oblique incidence of light source and different thickness of active layer.When the thickness of the active layer is 400nm,the short-circuit current density can reach 24.09 m A/cm²,which is very close to the theoretical absorption limit of 26.00 m A/cm².No matter from the point of view of absorption enhancement or mechanical tensile properties,the scheme of using composite light trapping structure to improve the absorption of thin-film solar cells has obvious advantages and is of great significance to the design and wide application of thin-film solar cells in the future.