SNM: Scalable Surface Corrugation of Silicon Surfaces for Enhanced Light Trapping in Solar Cells

太阳能光伏市场在全球范围内发展迅速。尽管增长迅速，安装光伏太阳能系统的成本必须进一步降低，以使太阳能在市场上广泛使用。难点在于如何在很大程度上降低材料成本和“软成本”，例如太阳能光伏组件的运输和安装。为了应对这一市场挑战，这个可扩展纳米制造（SNM）奖项将提供制造解决方案，通过首先使用薄而灵活的晶体硅衬底来降低材料成本，因为晶体硅占典型太阳能组件成本的30- 40%。薄基板的使用也将降低软成本，使电池能够支撑在一个轻量级的柔性平台上。轻量化意味着运输和安装成本的降低。虽然成本效益是显而易见的，但要保持薄硅太阳能电池同样的光伏效率，就需要在薄层内显著改善光捕获和吸收。要探索的技术解决方案是使用周期性的纳米级表面特征，减少对称性，有效地将阳光耦合到下面的硅衬底上。一种可制造的、具有成本效益的、高通量的工艺将被开发出来，以在硅薄膜上制造这种纳米结构。这种新工艺将在晶圆尺度上提供均匀性，在长度尺度上桥接六个数量级。该项目还将通过开发基于网络的沉浸式交互式可视化教育工具，帮助公众了解替代能源。在晶圆尺度上均匀地制造纳米尺度的特征提出了重大的工程挑战。目前存在各种光刻技术来定义亚微米特征。然而，任何一种技术的成功都将取决于其大规模性能和制造成本。例如，传统的深紫外光学步进器非常适合于太阳能电池中的亚微米光捕获功能，但对于晶圆级应用来说过于昂贵。研究小组将开发基于相位掩模的干涉光刻工艺，将相干光束投射到预图案化的光栅掩模上，并且从掩模中发出的衍射平面波相互干扰以形成周期图案。扩大规模的光刻工艺还将包括湿蚀刻步骤，以在薄硅太阳能电池上制造有效的光捕获结构。一个多尺度，多相输运和反应模型的湿蚀刻过程将发展，以解决规模扩大的工程挑战。本文将在器件层面上对所制备的大面积太阳能电池的光电特性进行研究。

Solar photovoltaics market is growing rapidly on a global scale. Notwithstanding the rapid growth, the cost of installed photovoltaic solar energy system must be further reduced for a wide distribution of solar power usage in the marketplace. The difficulty has been to reduce, by a significant degree, both the material cost and the "soft cost", such as transportation and installation of solar photovoltaic modules. Addressing this market challenge, this Scalable NanoManufacturing (SNM) award will provide manufacturing solutions to reduce the material cost by first making use of thin, flexible crystalline silicon substrates, as crystalline silicon accounts for as much as 30-40 percent of a typical solar module cost. The use of thin substrates would also reduce the soft cost by enabling cells to be supported on a lightweight flexible platform. Lightweight translates to reduced transportation and installation costs. While the cost benefits are clear, maintaining the same photovoltaic efficiency from thin silicon solar cells requires significantly improved light trapping and absorption within the thin layer. The technical solution to be explored is to use periodic, nanoscale surface features with reduced symmetry to effectively couple the sunlight into the underlying silicon substrate. A manufacturable, cost-effective, high-throughput process will be developed to fabricate such nanostructures on thin silicon films. This new process will provide uniformity over a wafer-scale, bridging six orders of magnitude in length scale. The project will also help the public appreciate alternative energy sources by developing educational tools using web-based immersive interactive visualization.Fabricating nanoscale features uniformly over a wafer scale poses significant engineering challenges. Various lithographic techniques exist today to define submicron features. However, the success of any one technique will depend on its large-scale performance and manufacturing cost. For instance, the conventional deep-UV optical steppers are highly suitable for sub-micron light-trapping features in solar cells but are overly expensive for wafer-scale applications. The research team will develop processes to scale up phase-mask-based interference lithography, where a coherent beam is projected on a pre-patterned grating mask, and the diffracted plane waves from the mask interfere with each other to make periodic patterns. The scale-up lithography processes will also involve wet etching steps to fabricate efficient light-trapping structures on thin silicon solar cells. A multiscale, multiphase transport and reaction model of the wet etch process will be developed to solve the scale-up engineering challenge. The photovoltaic characteristics of the large-area solar cells fabricated by the developed processes will be investigated on a device level.