EAGER: Unified Photon and Electron Harvesting Method for High Efficiency Thin-film Silicon Solar Cells

单晶硅仍然是利用太阳能的首选材料，因为它的天然丰度和上级电子性能。更薄的太阳能电池对于许多应用都很重要，例如为柔性电子产品供电。虽然薄硅更轻，但其光子吸收率低，因此限制了太阳能电池在不影响效率的情况下可以做得多薄。为了实现超薄（小于30微米）单晶硅太阳能电池，需要建立一种结合光子和电子传输的管理工艺，以实现约33%的理论效率极限。EARLY探索性研究（EAGER）奖将调查统一设计方法背后的科学，以最大限度地提高集体光子-电子捕获。该研究将实施统一的光子-电子收集机制，在25微米厚的单晶硅晶片上实现超过20%的能量转换效率，该晶片比目前的传统电池薄7倍。这将导致巨大的成本，重量和材料节省，以及实现灵活的太阳能模块。为了制造这些模块，将采用大面积纳米压印技术，该技术显示出达到分子水平的分辨率和再现性，这是薄膜内部有效的光子和电子传输所需的。多年来，光伏界一直在研究载流子寿命、表面钝化和复合机制，以提高硅太阳能电池的效率。类似地，光学界已经广泛地研究了各种光捕获机制以最大化光子吸收。显然，电子和光子的概念都遵循非常独立和有点相互排斥的路径。为了最大化太阳能电池效率，需要统一的光子-电子收集方法。光捕获机制，无论是基于光子效应还是等离子体效应，都会产生高吸收的局部“热点”，这会显著调制整个晶片上的电荷载流子生成速率。然而，所有现有的电池架构都假设均匀地产生电荷载流子，这不能利用这种光捕获，因此，即使具有高光子吸收，电池电效率仍然很低。这些是迄今为止还没有证明薄膜太阳能电池的高效率的一些原因。这项跨学科的研究工作将采用纳米压印大面积光捕获系统，结合多功能复合钝化和抗反射层，基于梯度掺杂的有效电荷分离和交叉指型电子收集系统，以最大限度地提高组合光子-电子收集，以创造接近33%的肖克利-奎瑟极限的高效薄膜太阳能电池。

Monocrystalline silicon remains the number one material of choice for harnessing solar energy due to its natural abundance and superior electronic properties. Thinner solar cells are important for many applications such as powering flexible electronics. While thin silicon is lighter, its photon absorption is low thus limiting how thin the solar cell can be made without compromising efficiency. In order to realize ultra-thin (less than 30 micron) monocrystalline silicon solar cells, a combined photon and electron transport management process needs to be established that will achieve the theoretical efficiency limit of about 33 percent. This EArly-Grant for Exploratory Research (EAGER) award will investigate the science behind a unified design approach in order to maximize collective photon-electron harvesting. The research will implement a unified photon-electron harvesting mechanism to achieve greater than 20 percent energy conversion efficiency in a 25-micron thick monocrystalline silicon wafer, which is about 7 times thinner than present conventional cells. This will result in enormous cost, weight and material savings as well as enabling flexible solar modules. To fabricate these modules, a large area nanoimprinting technique will be employed that is shown to reach molecular level of resolution and reproducibility, which are needed for efficient photon and electron transport inside the thin-film. For many years, the photovoltaic community has studied carrier life time, surface passivation and recombination mechanisms to improve efficiencies in silicon solar cells. Similarly, the optics community has extensively studied various light trapping mechanisms to maximize photon absorption. Evidently, both electronic and photonic concepts have followed very independent and somewhat mutually exclusive paths. A unified photon-electron harvesting method is needed in order to maximize solar cell efficiency. Light trapping mechanisms, whether based on photonic or plasmonic effects, create local "hot-spots" of high absorption, which significantly modulate the charge carrier generation rate across the wafer. However, all present cell architectures assume uniform generation of charge carriers, which fails to take advantage of such light trapping and hence, even with high photon absorption, the cell electrical efficiency remains low. These are some of the reasons that to date there has been no demonstration of high efficiency in thin-film solar cells. This inter-disciplinary research work will employ a nanoimprinted large area light trapping system in conjunction with multi-functional composite passivation and anti-reflection layer, a graded doping based efficient charge separation and an interdigitated electron collection system to maximize combined photon-electron harvesting in order to create high efficiency thin-film solar cells approaching the Shockley-Queisser limit of 33 percent.