Design And Performance Of Upconversion Crystalline Silicon Solar Cells Based On Sub-Wavelength Structures

Photovoltaic power generation is one of the key directions of future energy development,and the most widely used solar cells are silicon-based solar cells.The key to improving the photoelectric conversion efficiency of silicon-based solar cells lies in how to achieve high-efficiency absorption of light and enhancement of the photovoltaic effect.Sub-wavelength structures show great advantages in the field of light-trapping and efficiency enhancement of silicon based solar cells due to their special size effect that can enhance light-trapping.Upconversion materials can convert low-energy photons to high-energy photons,which can then be utilized by the solar cell.So the combination of solar cells with UC materials is the effective means to reduce these transmission losses.In this thesis,a combination of subwavelength structure and upconversion material is proposed for silicon based solar cells.Ultrathin upconversion crystalline silicon solar cells with subwavelength arrays such as sodium yttrium fluoride nanospheres,inverted nanocone holes and silver nanohemispheres are designed.The optical performance,electrical performance and frequency upconversion performance of the solar cells are calculated by finite element method and rate equation simulation.Besides,the mechanism of solar cells performance enhancement are discussed in combination with the effective refractive index,resonance mode and local surface plasmon resonance.Detailed description of the research was listed as following:Firstly,the physical property parameters of rare earth doped sodium yttrium fluoride materials are obtained by first-principles calculation.The optical properties,electrical properties and frequency upconversion properties of solar cells are calculated by finite element method and rate equation simulation.A simulation system of solar cells with subwavelength structure and frequency upconversion layer is designed and described.The“optical-frequency upconversion-electrical” coupling analysis is used to evaluate the photoelectric conversion efficiency of the cell.Secondly,the erbium-doped sodium yttrium fluoride nanosphere arrays are designed on surface of the ultrathin crystalline silicon solar cells based on the concept of light-trapping structure.The effect of the structure adjustment of nanosphere arrays on the light-trapping effect of solar cells is systematically studied by finite element method,and the optimal structure of the nanosphere arrays are determined.The upconversion effect of erbium-doped sodium yttrium fluoride on the photoelectric conversion efficiency of the solar cell was obtained by calculating the three level rate equation of erbium ions.Then,based on the principle of 2-D photonic crystal,an ultrathin crystalline silicon solar cell with the embedded inverted nanocone hole light-trapping structure is constructed.The influences of the diameter,spacing and apex angle change of inverted nanocone hole on the photoelectric performance of the solar cell are analyzed in detail.The effect of Erbium/Ytterbium co-doped sodium yttrium fluoride on the photoelectric efficiency of the solar cell are solved by calculating the four level rate equation of Erbium/Ytterbium ions,which can improves the accuracy of the simulation.Finally,based on the principle of local surface plasmon resonance,an ultrathin crystalline silicon solar cell with silver nanostructure array embedded in the up-conversion layer is designed.The effects of particle size and volume ratio of silver nanohemispheres on light absorption of crystalline silicon active layer and light field intensity in Erbium/Ytterbium co-doped sodium yttrium fluoride upconversion layer are analyzed by finite element method,and the optimal structural parameters of silver nanoparticles are determined.By analyzing the light field intensity gain spectra of silver nanoparticles with different shapes,it is found that the hexagonal packed silver nanoarrays have gain peaks in specific spectral range.The structure regulation of silver nanoparticles can achieve light field enhancement at specific wavelength,which contributes to the improvement of luminescence efficiency of the upconversion materials.