Study On Light-trapping Mechanism And Optical Properties Of High Absorption Efficiency Solar Cells

The effective utilization of solar energy can relieve the two social difficult problems of energy shortage and environment pollution.The solar cell can directly convert sunlight into electrical energy,but now it is not widely applied in our society.The major reason is too low conversion efficiency and too high production cost for solar cell.Therefore,improving conversion efficiency and reducing cost is and remains to be a direction and goal of photovoltaic technology development.The application of micro-/nano-structure in the photovoltaic devices can greatly reduce the thickness of the absorbing layer,thereby reducing the production cost.In order to improve the conversion efficiencies of solar cells,a great deal of research work has been focused on the new photovoltaic materials and light trapping structures.This thesis chooses light trapping structures of solar cells as the research object,the new trapping structures based on needle profile grating arrays(NPGAs)and inclined nanowire arrays(NWAs)are designed.In addition,the surface plasmon model of spherical metal particles also is built.Through numerical simulation,we conduct a study about optical properties and light-trapping mechanism.In this thesis,the main research contents and the results are as follows:Firstly,for the GaAs NPGAs,the influence of structure parameters such as taper angle,filling factor and height on the light absorption has been systematically studied.The light absorption performance of NPGAs is sensitive to its structure parameters.The optimized NPGAs can lead to broadband optical absorption enhancement throughout the wavelength range studied.The maximum absorption efficiency of NPGAs with optimal parameters can achieve 99%,which is over 20% higher than that of rectangular grating counterpart.Secondly,the inclined GaAs NWAs as light absorbing structure for solar cells are proposed.By using the finite element method(FEM),the influence of diameter and filling factor of inclined NWAs on the optical absorption properties is investigated,and the optimal geometric parameters of the proposed structure are determined.The absorption profiles at different wavelengths and angle-dependent properties of inclined NWAs are also evaluated.The optimized NWAs yields a maximum absorption efficiency of 95% and a photocurrent of 30.3mA/cm2,which is superior to the optical properties of vertical NWAs.This demonstrates the light-trapping ability enhancement of inclined NWAs.Finally,the light-trapping model of Ag metal particles surface plasmon with crystalline silicon as background material is established,and the effect of location,diameter and filling factor of metal particles on the optical properties of crystalline silicon thin film are analyzed.The results reveal that the light absorption of crystalline silicon is sensitive to the diameter and filling factor of metal particles,but not sensitive to its location.The diameter and filling factor mainly affect the number of absorption peaks of crystalline silicon absorption spectrum.The light-trapping mechanism at these absorption peaks is analyzed.Adding metal particles into crystalline silicon thin film can improve the light absorption ability of silicon absorbing layer.