CAREER: Toward Twenty Year Lifetime:Hermetic Sealing for Perovskite Solar Cells

摘要：非技术描述：虽然目前绝大多数太阳能电池都是基于硅技术，但生产成本和无法在卷对卷平台上实现制造掩盖了其高效率和长期可靠性。钙钛矿是自然界中发现的一种晶体矿物，它是一种潜在的优越太阳能技术。钙钛矿太阳能电池的效率已经接近硅电池。然而，目前的钙钛矿太阳能电池由于毒性问题（铅通常用于制造钙钛矿）和寿命短而无法使用。该研究项目的目标是合成一种高效、经济、环保的锗钙钛矿太阳能电池。除了用化学性质相似但无毒的锗代替铅外，还将探索无机层，如氧化镍和氧化锡，作为界面层以提高稳定性。这些设备还将采用薄膜封装剂密封，并通过加速测试来确定设备的使用寿命。铅钙钛矿在理想的实验室条件下只能维持几个月。所提出的密封技术将使模块的使用寿命超过20年。这些电池在柔性衬底上制造的能力将进一步降低太阳能的价格，帮助太阳能变得比化石燃料衍生能源更便宜。该项目将为研究生、本科生、K-12和代表性不足的群体提供多种参与下一代可再生能源研究的机会。一门关于未来能源材料的新课程将使广大对材料科学和薄膜器件感兴趣的学生受益。这项工作的发现将使研究界对这种新型钙钛矿材料的基本特性有更深入的了解，并为工业提供商业化所需的信息。技术描述：在这项工作中，将合成钙钛矿锗，以构建高效、稳定、环保的太阳能电池。所提出的锗钙钛矿将克服铅基钙钛矿的缺点，包括毒性、界面层不稳定和有限的寿命。本项目分为两部分：通过薄膜封装剂和无机界面层的选择，合成并表征高质量的钙钛矿锗。锗钙钛矿具有高光吸收、高载流子迁移率和直接带隙等优异的光电性能。然而，先前的尝试由于膜形态不佳而失败。溶剂工程方法将用于获得高质量的锗基钙钛矿。钙钛矿的界面电荷传输层在本质上是无机的，以允许比有机层更大的器件稳定性。固体还原性气氛将用于防止由于水分和水随时间缓慢渗入而对钙钛矿造成氧化损伤。此外，原子层沉积（ALD）生长的金属氧化物屏障将覆盖成品装置，然后是最终的环氧树脂密封。由此产生的密封将通过氦和钙泄漏测试来表征，从中可以推断出预期的模块寿命。这种密封技术有望使设备的使用寿命超过20年。这项工作将为锗钙钛矿合成提供基本的理解，模拟封装太阳能器件的寿命，并在实现稳定，低成本和环境安全的太阳能电池方面发挥关键作用。

Abstract:Non-technical description: While the vast majority of current solar cells are based on silicon technology, the cost of production and inability to achieve fabrication in a roll-to-roll platform overshadow its high efficiency and long-term reliability. A potentially superior solar technology is based on perovskites, which are crystalline minerals found in nature. Perovskite solar cells have already achieved efficiencies close to that of silicon cells. However, current perovskite solar cells are not usable due to toxicity concerns (lead is generally used to fabricate perovskites) and short lifetimes. The goal of this research project is to synthesize an efficient, affordable, and environmentally safe germanium perovskite solar cell. In addition to replacing lead by chemically similar but non-toxic germanium, inorganic layers, such as nickel oxide and tin oxide, will be explored as interfacial layers to improve stability. The devices will also be hermetically sealed with thin-film encapsulants, and characterized through accelerated testing to determine device lifetime. Lead perovskites have only lasted several months under ideal laboratory conditions. The proposed sealing techniques will enable module lifetimes to be greater than 20 years. The ability of these cells to be fabricated on a flexible substrate will further drive down the price of solar energy, helping solar energy to become less costly than fossil fuel derived energy. This project will provide multiple opportunities for graduate, undergraduate, K-12, and under-represented groups to engage in the next generation of renewable energy research. A new course on future energy materials will benefit a broad range of students with interest in material science and thin film devices. The findings of this work will provide the research community with a greater understanding of the fundamental properties of this new perovskite material, and provide industry with the information needed for commercialization.Technical description: In this work, germanium perovskite will be synthesized to build highly efficient, stable, and environmentally benign solar cells. The proposed germanium perovskites will overcome the deficiencies of lead-based perovskites including toxicity, interfacial layer instability, and limited lifetime. The project is two-fold: high quality germanium perovskite will be synthesized and characterized and then stabilized through thin-film encapsulants and inorganic interfacial layer selection. Germanium perovskites display excellent photovoltaic properties such as high optical absorption, high carrier mobility, and direct band gap. However, previous attempts were unsuccessful due to poor film morphology. A solvent-engineering approach will be used to achieve high-quality germanium-based perovskite. The perovskite's interfacial charge transport layers will be inorganic in nature to allow for greater device stability than can be achieved with organic layers. A solid-state reducing atmosphere will be used to prevent oxidative damage to the perovskite due to slow ingression of moisture and water over time. In addition, atomic layer deposition (ALD) grown metal-oxide barriers will cap the finished device, followed by a final epoxy sealing. The resulting hermetic seal will be characterized through helium and calcium leak tests, from which the expected module lifetime can be extrapolated. This sealing technique is anticipated to enable device lifetimes in excess of 20 years. The proposed work will provide a fundamental understanding of germanium perovskite synthesis, model the lifetime of encapsulated solar device, and play a critical role in achieving stable, low-cost, and environmentally safe solar cells.