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

太阳能光伏市场正在全球范围内快速增长。尽管增长迅速，但安装的光伏太阳能系统的成本必须进一步降低，以便在市场上广泛分布太阳能的使用。困难在于大幅降低材料成本和“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，可伸缩纳米制造(SNM)奖将提供制造解决方案，通过首先使用薄而灵活的晶硅衬底来降低材料成本，因为晶硅占典型太阳能组件成本的30%-40%。使用薄衬底还将通过使电池能够支撑在轻质灵活的平台上来降低软成本。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的相同光伏效率，就需要显著改善薄层内的光捕获和吸收。要探索的技术解决方案是使用对称性降低的周期性纳米级表面特征，以有效地将阳光耦合到下面的硅衬底中。将开发一种可制造的、低成本的、高通量的工艺来在薄膜硅上制备这种纳米结构。这一新工艺将在晶片规模上提供一致性，将长度尺度上的六个数量级连接起来。该项目还将通过开发基于网络的沉浸式交互可视化的教育工具来帮助公众欣赏替代能源。在晶片规模上统一制造纳米级特征带来了巨大的工程挑战。今天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，传统的深紫外光步进器非常适合太阳能电池中的亚微米捕光功能，但对于晶片规模的应用来说过于昂贵。该研究小组将开发放大基于相位掩模的干涉光刻的工艺，其中相干光束投射到预制图案的光栅掩模上，来自掩模的衍射平面波相互干扰，形成周期性图案。放大的光刻工艺还将包括湿法刻蚀步骤，以在薄硅太阳能电池上制造高效的捕光结构。将开发一个多尺度、多相的湿法刻蚀过程的传输和反应模型，以解决放大的工程挑战。通过开发的工艺制造的大面积太阳能电池的光伏特性将在器件水平上进行研究。

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.