【作者】 丁超；

【导师】 李相银；

【作者基本信息】 南京理工大学 ， 光学工程， 2012， 硕士

【摘要】 薄膜太阳能电池作为下一代光伏器件最具有竞争力的角色,它们具有低成本、可实现柔性衬底上沉积以及易于发展光伏建筑一体化(BIPV)等特点。最近几年,特别是微晶硅(μc-Si：H)太阳能电池已经得到广泛的关注。最高稳定效率为10.3%的薄膜微晶硅太阳能电池已经研制成功。但是,因为微晶硅太阳能电池的厚度的非常薄,典型的厚度仅有0.8-1.5μm,且在长波长(600nm-1100nm)范围的吸收系数很低。为了增加薄膜微晶硅太阳能电池长波长波段光吸收,有效地陷光结构是非常必要的。如何得到最佳的陷光结构,改善薄膜微晶硅太阳能电池的性能具有很现实的意义。本文在集成随机织绒陷光结构的薄膜微晶硅太阳能电池模型基础上,采用亚微米周期结构(一维三角光栅)作为微晶硅太阳能电池的陷光结构,通过数值计算优化光栅结构,分析光栅结构参数对薄膜微晶硅太阳能电池在长波长波段相关性能的影响并获得合适的光栅结构参数。然后,通过实验手段在铝基底上自组装形成亚微米周期凹槽型结构,分析该结构的光学性质,探索其作为薄膜微晶硅太阳能电池的背表面反射器的潜在陷光性能。主要工作内容及结论如下：第一部分提出用于薄膜微晶硅太阳能电池陷光结构的亚微米周期性结构,即1D亚微米三角光栅。采用严格耦合波理论(RCWA)分析光栅的光学性质,研究光栅参数对其漫反射特性的影响。调节光栅结构参数,包括光栅周期和高度,得到漫反射性能较好的光栅参数。利用所得光栅结构参数,采用时域有限差分(FDTD)法评估不同的光栅周期和高度在600nm-1100nm波长范围内对薄膜微晶硅太阳能电池的光吸收、量子效率、短路电流的影响,并与平面结构作比较。最后得到光栅周期在800nm,高度为300nm时,微晶硅太阳能电池的短路电流值最大,相比于平面结构增加了3.8 mA/cm2。相比于微米级矩形光栅结构,最大短路电流提高了11.6个百分点,证明了一维亚微米三角光栅的陷光性能更有效。第二部分采用铝阳极氧化方法,成功地在铝基底上自组装了亚微米周期凹槽型结构,并将该结构应用于薄膜微晶硅太阳能电池背表面反射陷光结构,分析其潜在的陷光性能。通过改变阳极氧化电压,得到三组不同周期的背表面反射器。采用扫描电子显微镜观察样品表面形貌和微结构,得到凹槽周期和深度大小。通过紫外可见近红外分光光度计测量了样品的漫反射性质,分析了样品周期大小与背表面反射结构光散射特性包括绒度系数、角散射分布等的关系。最后得到,随着周期的增大,样品的光散射特性越好；当凹槽周期为600nm时,光散射强度甚至超过Asahi-U型结构。这一结果显示,使用大周期凹槽结构作为薄膜太阳能电池背表面反射器时,将呈现出更加优越的陷光性能,更有效地改善薄膜太阳能电池的性能。更多还原

【Abstract】 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.更多还原