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

单晶硅由于其天然的丰度和优异的电子性能，仍然是利用太阳能的首选材料。更薄的太阳能电池对许多应用都很重要，比如为柔性电子产品供电。虽然薄硅较轻，但其光子吸收较低，因此在不影响效率的情况下限制了太阳能电池的厚度。为了实现超薄(小于30微米)单晶硅太阳能电池，需要建立一种光子和电子相结合的管理工艺，以达到理论上约33%的效率极限。这项早期探索研究资助奖将调查统一设计方法背后的科学，以便最大限度地集体收集光子-电子。这项研究将实施统一的光子-电子捕获机制，以在25微米厚的单晶硅晶片中实现20%以上的能量转换效率，这一厚度约为目前常规电池的7倍。这将带来巨大的成本、重量和材料节约，并实现灵活的太阳能组件。为了制造这些模块，将采用大面积纳米印迹技术，该技术将被证明达到分子水平的分辨率和重复性，这是在薄膜内高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、表面钝化和复合机制，以提高硅太阳能电池的效率。同样，光学界也广泛研究了各种光捕获机制，以最大限度地吸收光子。显然，电子学和光子学的概念都走上了既非常独立又有些互斥的道路。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捕获方法。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”，从而显著调节整个晶片的载流子产生率。然而，所有现有的电池结构都假设均匀地产生电荷载流子，这未能利用这种光捕获，因此，即使具有高的光子吸收，电池的电效率仍然很低。这些都是到目前为止还没有证明薄膜太阳能电池具有高效率的部分原因。这项跨学科的研究工作将采用纳米印迹大面积光捕获系统，结合多功能复合钝化和减反射层、基于分级掺杂的高效电荷分离和交指电子收集系统，以最大限度地结合光子和电子收集，从而创造出接近33%的Shockley-Queisser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.