Study Of Design And Experiment Of Periodic Light-Trapping Structures With Submicrometer In Thin-film Microcrystalline Silicon Solar Cells

Thin-film solar cells(TFSC) are promising candidates for future generations of photovoltaic devices. They offer cost effectiveness, possibility of deposition on flexible substrates and easier deployment and better integration into buildings. In particular, hydrogenated microcrystalline silicon(μc-Si:H) solar cells have gained considerable attention in recent years. Efficiencies higher than 10% have been demonstrated for microcrystalline silicon solar cells. Since the solar cell is very thin, with typical absorber thicknesses of 0.8-1.5μm and low absorption coefficient in the red and near-infrared wavelength(600nm-1100nm) ranges, efficient light trapping concepts are needed to increase the absorption of the long wavelength light within the solar cell. How to find the optimized structure for efficient light trapping of longer wavelength light has significant meaning of reality for improving performance of microcrystalline thin-film silicon solar cells.In this paper, based on model ofμc-Si:H TFSC with an integrated randomly textured interfaces, submicrometer periodic textured was introduced, which act as the light trapping configuration ofμc-Si:H TFSC. To investigate the light propagation in the cells, especially in the longer wavelength region, two-dimmensioned power loss profiles are simulated. The influence of different structure parametres—such as period size and height—was studied to determine an optimized light trapping scheme. Then, back surface reflectors with grating structures was fabricated by self-assembled porous alumina for light trapping in silicon solar cells. And the potential performance of light trapping as back reflectors ofμc-Si:H TFSC is evaluated by analyzing the optical properties of the structure. The research contents and results can be summarized as follows:(1) It is reported that the highest efficiencies have been achieved by introducing randomly textured interfaces in the thin-film solar cells. Hence, with the purpose of obtaining both higher efficiency and simple light trapping structures, we introduce submicrometers periodic structure (ie, submicrometers triangular grating)for light trapping ofμc-Si:H TFSC. Influence of grating dimensions on the optical properties ofμc-Si:H TFSC was studied by the numerical simulation, especially in the long wavelength band. Firstly this study analyses the diffuse reflection properties of different grating parameters by Rigorous Coupled Wave Analysis to explore its property of light trapping. Then the finite difference time domain algorithm was used to investigated the effect of grating parametres—such as grating period and height—on the power loss, quantum efficiency, and short circuit current of microcrystalline silicon solar cells. The simulation show that the grating structure leads to scattering and higher order diffraction, which increases the effective thickness of solar cell and results in an increased absorption of the incident light inμc-Si:H TFSC. Compared to that of solar cell on a flat surface, integrated grating leads to a distinctly enhanced quantum efficiency and short circuit current in red and near-infrared parts of the sun spectrum. Optimal dimensions of the submicrometers grating were received.(2) On the basis of above study, performance of light trapping of back surface reflectors with grating structures for thin-filmμc-Si:H soalr cells were invertigated. We utilize anodic oxidation of aluminum as a self-assembled process to prepare back surface reflectors with grating structures to enhance light trapping. By changing the anodic oxidation condition, self-orderd periodic dimple pattern with different period size has been fabricated on aluminum substrate. The surface morphology of Al substrates was characterized by scanning electron microscope (SEM). To evaluate potential performance of light trapping of back surface reflectors with periodic dimple pattern, light scattering parameters—haze factor and angular resolved scattering—of the substrates were determined using total integrated scattering and angular distribution of the reflected light intensities. Moreover, the relationship between the period of substrates and the potential light-trapping effect inμc-Si:H cells is discussed, and the optimum size is determined. For comparison, light scattering properties of the flat and Asahi-U type substrates are also shown.