Theoretical And Experimental Study Of Silicon Nanoparticles To Enhance The Efficiency Of Solar Cells

At present,carbon peaking and carbon neutrality have increasingly become a common concern of the whole society.China’s current energy structure is still mainly based on fossil energy,so the transformation and upgrading of the energy structure has become an unstoppable trend.Among them,the sun is the main source of energy,almost all forms of energy on earth come from it,solar energy because it is an endless source of energy,with no pollution and no security risks.It could be the answer to energy problems in the next few centuries.Harnessing solar energy through solar cells is an important and effective method with a high potential for future energy development.For solar cells,one of the most important ways to increase the efficiency of solar cells is to improve the absorption of sunlight.The use of silicon nanoparticles in siliconbased solar cells had attracted the interest of researchers due to its excellent optical and electrical properties.The optical coupling of silicon nanoparticles to the surface of solar cells is a technology that facilitates large-scale use as no other elements are introduced externally.And the controlled optical properties of silicon nanofilms formed from silicon nanoparticles could better improve the light absorption of solar cells.In view of the above status and problems,this thesis explored the model analysis and theoretical calculations of silicon nanofilms as anti-reflective films for solar cells,demonstrating that the efficiency of monocrystalline silicon solar cells could be effectively improved by controlling the porosity and thickness of silicon nanofilms.It provided guidance and direction for experimentation.Meanwhile,this thesis was based on self-developed silicon nanoparticles(Si NPs)with a core-shell structure that could be prepared macroscopically in combination with organic solvents.Using the spin-coating method,the light absorption of the solar cells was improved by regulating the concentration of the silicon nanoparticles,the thickness of the silicon nanofilms,and the porosity.As an anti-reflective surface for monocrystalline silicon solar cells,it was demonstrated that this gain came from the additional absorption of light by the silicon nanofilm.Also,the experimental and theoretical models matched well.The application of refractive indexcontrolled silicon nanofilms in solar cells was investigated from both theoretical simulations and experimental perspectives.At the same time,with further modification of the nanosilicon,it was possible to improve its down-conversion effect and the efficiency of solar cells would be further enhanced.The relevant studies are as follows:(1)Model design and theoretical study of silicon nanofilm anti-reflective coatings:The effective absorption of sunlight by silicon nanofilms of different porosity and thickness could affect the efficiency of solar cells.In order to investigate the intrinsic mechanism of solar cell efficiency improvement and also to provide accurate predictions for the preparation of silicon nanofilms.The Transfer matrix method(TMM),finite difference time domain method(FDTD)and Silvaco TCAD simulations were used to analyze the effect of reflection and other electrical properties of the silicon nanofilms on the surface of the solar cell.The simulation results showed that the silicon nanofilm with a porosity of 85% and thickness of 110 nm had the most significant effect on the efficiency of the solar cell,with a relative increase in short-circuit current of3.61%.This was also close to the optimum thickness calculated from the optical reflective film design guidelines.It suggested that it was accurate to rely on this guideline in testing.This work calculated the optimum model applicable to the experimental results from a reasonable evaluation of the effective medium theory and ray-tracing models respectively.Through optical and electrical simulations,guidance,predictions and interpretations could be provided for subsequent experiments.(2)Preparation and anti-reflective properties of silicon nanoparticles and silicon nanofilms:Homogeneous spherical silicon nanoparticles with a regular shape and an average particle size of about 56 nm were prepared by the mass production nanopowder(MPNP)technology developed by our group.The nanoparticles were mixed with an organic solvent,isopropanol,and the nanoparticles were uniformly dispersed to obtain the silicon nanogel.Porous silicon nanofilms were obtained on the surface of solar cells by the spin coating method.In order to obtain silicon nanofilms with different thicknesses and porosities,the concentration of the silicon nano gel and the speed of spin coating as well as the number of layers need to be adjusted.The morphological characterization showed a porous nanofilm structure on the surface of the solar cell,using the passivated layer as a substrate.The silicon nanofilms had a porous "trapped light structure" inside and the particles were no longer regular in shape.At a concentration of 0.1 mg/ml,deposition of three layers of silicon nanofilms,the absolute efficiency value of the solar cell was increased by 0.23% and the short-circuit current was increased from 170.53 m A to 172.43 m A.This work discussed the role of silicon nanofilms in improving the performance of solar cells from various aspects such as microstructure,performance testing,and coordination effects.The rational design and application of porous structured silicon nanofilms in solar cell anti-reflection films were demonstrated from an experimental perspective.(3)Surface modification of silicon nanoparticles and further enhancement of solar cell efficiency:In order to further improve the efficiency of the solar cell,the surface modification of the silicon nanoparticles was used to enhance the "down-conversion effect" of the silicon nanoparticles themselves.The synergistic effect was used to improve the efficiency of the solar cell in combination.The oxide layer on the surface of the silicon nanoparticles was removed by washing with hydrofluoric acid.Subsequently,the surface modification of the cleaned silicon nanoparticles was carried out using styrene,which further increased the efficiency of the solar cell by 0.30% in absolute terms.At the same time,the oxidation of the surface of the silicon nanoparticles was inhibited by a hydrosilylation reaction to improve the stability of the silicon nanofilms.Although,over time,the surface-modified silicon nanoparticles themselves still were still slowly oxidized.But ultimately it was still superior to the effect before modification.