EAGER: Transparent electrode device architecture for high efficiency tandem colloidal quantum dot photovoltaics

摘要非技术性的出现，重量轻，灵活，高效，负担得起的太阳能电池模块可能会彻底改变能源发电从太阳。在竞争的技术中，采用硫化铅纳米晶薄膜的光致发光技术的效率一直在以前所未有的最快速度增长。然而，两个方面限制了这些电池的效率：电子可以通过硫化铅薄膜移动多远以及纳米晶体中存在多少材料缺陷。串联太阳能电池（多个太阳能电池彼此堆叠生长）可以避免这些限制，因为多个薄电池可以堆叠在一起，以实现整个电池的强吸收。令人惊讶的是，以前尝试使用硫化铅纳米晶体制造两层串联光致发光器件没有实现预期的效率的显著提高。该项目提供的建模数据显示，在观察到效率的显著提高之前，至少必须堆叠五层电池。将制造一个由两个太阳能电池与透明导电金属氧化物层连接组成的主要证明设备。这项研究将在霍利奥克山学院进行，这是一所女子本科学院，在科学领域有着卓越的教育女性的历史。技术PI将制造一种串联结构的硫化铅胶体量子点光伏，以增强太阳光谱中关键长波长区域的吸收。在过去的十年中，胶体量子点光电子器件的功率转换效率已经取得了巨大的进步，但许多最好的器件仍然存在红外吸收低的问题，这是第一激子跃迁峰处振子强度弱的结果，通常导致吸收减少50%以上。 载流子扩散长度（范围约100 nm）和吸收可观量的太阳光谱所需的厚度（范围约500 nm）之间的失配导致吸收不足。 初步建模表明，五结串联结构可以实现完全吸收，同时允许每个子电池中硫化铅层的最大厚度保持在100 nm以内，实现了直接的、可实现的途径，实际效率接近19%，理论效率接近28%。 串联结构是一种有效的增加吸收的方法，已经在小分子有机光伏和其他地方使用，但以前从未有研究人员组装有效构建五个或更多串联结所需的工具。 PI将通过采用定制的低损伤溅射技术在复合区沉积金属氧化物传输层和透明导体来制造原理验证串联结构，集成光纤分光光度计用于精确的吸收测量，再加上仔细的光学建模，用于无缝器件制造的互连手套箱系统，以及革命性的热反射成像技术，用于绘制电流和电场不均匀性。

AbstractNontechnical The emergence of lightweight, flexible, efficient, and affordable solar cell modules could revolutionize energy generation from the sun. Among the contending technologies, photovoltaics employing lead sulfide nanocrystalline films have been increasing in efficiency at one of the most rapid paces ever seen. However, two aspects limit the efficiency of these cells: how far electrons can move through the lead sulfide film and how many material defects exist in the nanocrystals. Tandem solar cells (multiple solar cells grown on top of one another) can circumvent these limitations because multiple thin cells can be stacked to achieve strong absorption across the whole cell. Surprisingly, previous attempts at fabricating two-layer tandem photovoltaics using lead sulfide nanocrystals have not achieved the dramatic gains in efficiency that would be expected. This project presents modeling data showing that at least five layers of cells must be stacked before significant enhancements in efficiency will be observed. A proof-of-principal device will be fabricated consisting of two solar cells connected with a transparent conducting metal oxide layer. The research will take place at Mount Holyoke College, a women's undergraduate college with a remarkable history of educating women in the sciences.TechnicalThe PI will fabricate a lead sulfide colloidal quantum dot photovoltaic in a tandem structure in order to enhance absorption in the critical long-wavelength region of the solar spectrum. Dramatic gains in the power conversion efficiency of colloidal quantum dot photovoltaics have been achieved over the past decade, but many of the best devices still suffer from low absorption in the infrared, a consequence of weak oscillator strength at the first excitonic transition peak, often resulting in more than a 50% reduction in absorption alone. The mismatch between the carrier diffusion length (ranging around 100 nm) and the thickness needed to absorb an appreciable amount of the solar spectrum (ranging around 500 nm) accounts for the shortfall in absorption. Preliminary modeling demonstrates that a five-junction tandem structure can achieve full absorption while allowing the maximum thickness of the lead sulfide layer in each sub cell to stay within 100 nm, achieving a straightforward, attainable pathway to realistic efficiencies approaching 19% and theoretical efficiencies approaching 28%. Tandem structures are an effective method of increasing absorption already employed in small molecule organic PV and elsewhere, but never before have had researchers assembled the tools needed to effectively construct five or more tandem junctions. The PI will fabricate a proof-of-principle tandem structure by employing a custom low-damage sputtering technique for the deposition of metal oxide transport layers and transparent conductors at the recombination zone, an integrated fiber-optic spectrophotometer for accurate absorption measurements coupled with careful optical modeling, an interconnected glovebox system for seamless device fabrication, and a revolutionary Thermo-reflectance imaging technique to map current flow and electric field non-uniformities.