Advanced methods for light trapping in optically thin silicon solar cells
Advanced methods for light trapping in optically thin silicon solar cells
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光学薄硅太阳能电池中光捕获的先进方法
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发表时间：
2011
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通讯作者：
J. Nagel
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作者：
J. Nagel
光阱领域是研究当大多数光在表面反射或直接透射到另一面时，如何在材料薄膜中最好地吸收光。这在光子学领域有巨大的应用，在光子学领域，薄硅膜可以便宜地制造，但也不能捕获太阳光谱中所有可用的光子。因此，光捕获技术的进步使我们更接近光伏器件在电能市场上与传统化石燃料实现电网平价的那一天。本论文首先模拟了平面介质波导中的损耗效应，从而推进了对光陷的理解。这里开发的数学框架可以用来模拟任何任意的三层结构的混合增益或损失，然后提取的引导模式的总场解。结果发现，有耗波导具有更多的本征模比他们的无损同行，这些“损耗引导”模式衰减得更快，比传统的模式。本论文的另一个贡献是通过使用直接嵌入在薄硅膜的有源层内的介电纳米球来探索光捕获。这种方法的主要好处是，该器件可以利用表面氮化物层作为抗反射涂层，同时仍然保留在膜内捕获光的好处。最终结果是光捕获和光注入彼此有效地解耦，并且可以在单个光伏器件内独立地优化。这项工作的最后贡献是多个光捕获方案之间的直接数值比较。这使我们能够量化各种设计技术彼此之间的相对性能，并客观地确定哪些想法倾向于捕捉最多的光线。使用数值模拟，这项工作直接比较了由于嵌入的纳米颗粒，表面纹理，抗反射涂层和等离子体纳米球的吸收增益。这项工作还介绍了一个新的数学度量区分折射率匹配和角散射在纹理表面。这些信息将被证明是有用的，在指导未来的科学努力，在光捕获和光管理领域的薄膜光致发光。
The field of light trapping is the study of how best to absorb light in a thin film of material when most light either reflects away at the surface or transmits straight through to the other side. This has tremendous application to the field of photovoltaics where thin silicon films can be manufactured cheaply, but also fail to capture all of the available photons in the solar spectrum. Advancements in light trapping therefore bring us closer to the day when photovoltaic devices may reach grid parity with traditional fossil fuels on the electrical energy market. This dissertation advances our understanding of light trapping by first modeling the effects of loss in planar dielectric waveguides. The mathematical framework developed here can be used to model any arbitrary three-layer structure with mixed gain or loss and then extract the total field solution for the guided modes. It is found that lossy waveguides possess a greater number of eigenmodes than their lossless counterparts, and that these “loss guided” modes attenuate much more rapidly than conventional modes. Another contribution from this dissertation is the exploration of light trapping through the use of dielectric nanospheres embedded directly within the active layer of a thin silicon film. The primary benefit to this approach is that the device can utilize a surface nitride layer serving as an antireflective coating while still retaining the benefits of light trapping within the film. The end result is that light trapping and light injection are effectively decoupled from each other and may be independently optimized within a single photovoltaic device. The final contribution from this work is a direct numerical comparison between multiple light trapping schemes. This allows us to quantify the relative performances of various design techniques against one another and objectively determine which ideas tend to capture the most light. Using numerical simulation, this work directly compares the absorption gains due to embedded nanoparticles, surface textures, antireflective coatings, and plasmonic nanospheres. This work also introduces a new mathematical metric for differentiating between index matching and angular scattering at a textured surface. Such information will prove useful in guiding future scientific efforts in the fields of light trapping and light management in thin film photovoltaics.