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是基于硅技术的，但生产成本和无法在卷到卷平台上实现制造，使其高效率和长期可靠性黯然失色。一种潜在的优越太阳能技术是基于钙钛矿，这是一种在自然界中发现的结晶矿物。钙钛矿型太阳能电池已经达到了接近硅电池的效率。然而，目前的钙钛矿太阳能电池由于毒性问题(铅通常用于制备钙钛矿)和较短的寿命而无法使用。本研究项目的目标是合成一种高效、经济、环保的钙钛矿锗太阳能电池。除了用化学上相似但无毒的锗取代铅外，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。这些设备还将用薄膜密封剂进行密封，并通过加速测试来确定设备的寿命。在理想的实验室条件下，铅钙钛矿只持续了几个月。建议的密封技术将使模块寿命超过20年。这些电池可以在柔性衬底上制造，这将进一步压低太阳能的价格，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参与下一代可再生能源研究的多个机会。一门关于未来能源材料的新课程将使对材料科学和薄膜器件感兴趣的广泛的学生受益。这项工作的结果将使研究界更好地了解这种新的钙钛矿材料的基本性质，并为业界提供商业化所需的信息。技术说明：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。所提出的锗钙钛矿材料将克服铅基钙钛矿材料的毒性、界面层不稳定性和寿命有限等不足。该项目包括两个方面：合成高质量的锗钙钛矿，并对其进行表征，然后通过薄膜包覆剂和无机界面层的选择进行稳定。锗钙钛矿具有高的光吸收、高的载流子迁移率和直接带隙等优良的光伏性能。然而，由于薄膜形态较差，以前的尝试都没有成功。将使用溶剂工程的方法来获得高质量的锗基钙钛矿。钙钛矿的界面电荷传输层本质上将是无机的，从而允许比使用有机层实现更大的设备稳定性。将使用固态还原气氛来防止由于水分和水随着时间的推移缓慢渗入而对钙钛矿造成的氧化损害。此外，原子层沉积(ALD)生长的金属氧化物屏障将覆盖完成的器件，随后是最终的环氧胶密封。由此产生的密封将通过氦和钙泄漏测试来表征，由此可以推断模块的预期寿命。这种密封技术有望使设备寿命超过20年。这项工作将提供对锗钙钛矿合成的基本了解，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.