SBIR Phase I: Subwavelength Structures for Enhanced Absorption in Thin Silicon Films

这个小企业创新研究（SBIR）一期项目将开发薄膜（小于50微米）晶体硅（Si）光伏（PV）电池。目前，硅晶片约占全部光伏组件成本的50%。微弱的近红外吸收需要250微米厚的硅薄膜来吸收可用的光辐射。初步计算表明，适当设计的亚波长结构可以在20-50微米厚的薄膜上实现相当的吸收。这些亚波长结构现在可以使用最新进展的Si反应离子蚀刻（DRIE）技术来制造。DRIE技术的初步测试表明，对于小于1微米的光栅周期，纵横比（深度与线宽）大于30。第一阶段将探索从传统硅衬底上剥离微结构薄膜的技术。将剥离膜粘合到用于后续太阳能电池加工的低成本衬底上。原始晶圆经过简单的平面化步骤后可重新使用。同一硅片的几个提升步骤将抵消增加的加工成本，并允许节省硅材料成本。该基础技术有望在纳米结构Si衬底上的异质外延生长中找到应用。这种薄膜硅太阳能电池技术的新方法有望实现商业应用。

This Small Business Innovation Research (SBIR) Phase I project will develop thin film (less than 50 microns) crystalline silicon (Si) photovoltaic (PV) cells. At present, Si wafers account for approximately 50 per cent of the completed PV module cost. Weak near-infrared absorption requires 250-micron thick Si films to absorb available optical radiation. Preliminary calculations indicate that appropriately designed subwavelength structures can achieve comparable absorption in films 20-50 microns thick. These subwavelength structures can now be fabricated using recent advances in Si reactive ion etching (DRIE) technology. Preliminary tests with DRIE techniques have demonstrated aspect ratios (depth to linewidth) greater than 30 for grating periods less than 1 micron. Phases I will explore a technique of microstructured thin films lift-off from a conventional Si substrate. The lift-off film is bonded to a low-cost substrate for subsequent solar cell processing. Original wafers are re-used following a simple planarization step. Several lift-off steps from the same Si wafer will offset added processing costs and permit savings in Si material costs.The underlying technology is expected to find applications in homo- and hetero-epitaxial growth on nanostructured Si substrates. Commercial applications are anticipated in this new approach to thin film Si solar cell technology.