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优越的电子性能。更薄的太阳能电池对许多应用都很重要，比如为柔性电子设备供电。虽然薄硅更轻，但它的光子吸收很低，因此限制了在不影响效率的情况下制造太阳能电池的厚度。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过程，该过程将达到约33%的理论效率极限。这项探索性研究早期拨款（EAGER）奖将研究统一设计方法背后的科学，以最大限度地实现集体光子电子收获。该研究将实现统一的光子电子收集机制，在25微米厚的单晶硅片上实现超过20%的能量转换效率，单晶硅片比目前的传统电池薄约7倍。这将导致巨大的成本，重量和材料的节省，以及使灵活的太阳能组件。为了制造这些模块，将采用大面积纳米压印技术，该技术将达到分子水平的分辨率和再现性，这是薄膜内有效的光子和电子传输所必需的。多年来，光伏界一直在研究载流子寿命、表面钝化和重组机制，以提高硅太阳能电池的效率。同样，光学学界也广泛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相互排斥的路径。为了最大限度地提高太阳能电池的效率，需要一种统一的光电子收集方法。无论是基于光子还是等离子体效应的光捕获机制，都会产生高吸收的局部“热点”，从而显著调节晶圆上载流子的产生速率。然而，目前所有的电池结构都假设电荷载流子的产生是均匀的，这不能利用这种光捕获，因此，即使具有高光子吸收，电池的电效率仍然很低。这就是迄今为止薄膜太阳能电池还没有证明其高效率的一些原因。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，基于梯度掺杂的高效电荷分离和交叉电子收集系统，以最大限度地结合光子电子收集，从而创造出接近肖克利-奎瑟极限33%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.