Emergent Opto-Mechanical and Electro-Mechanical Coupled Behavior of Halide Perovskites

所谓的“卤化物钙钛矿”是一种新型太阳能电池技术的核心材料。这些新的太阳能电池显示出巨大的希望，因为它们不仅能高效地将太阳光转化为电能，而且制造成本也很低。然而，这些新型太阳能电池材料的机械性能尚不清楚，特别是在太阳能电池的工作条件下：在阳光下，以及电流通过它们时。因此，研究和了解这些特性是非常重要的，因为它们决定了新的太阳能电池的长期耐用性，这些电池有望在元素中有效运行20年或更长时间。为此，进行了系统的研究，研究了新型太阳能电池材料在光和/或电流作用下的以下相关力学性能：(1)裂纹的开裂和愈合；(2)塑性变形；(3)随时间变形。这些研究是在化学成分、结构和形态明确的材料上进行的。这些研究的结果被批判性地分析，以了解新的太阳能电池材料的行为。预计这将对未来制造高耐用、低成本太阳能电池的能力产生广泛影响，并帮助这种新的太阳能电池技术充分发挥其潜力。作为这项努力的一部分，来自图加卢学院的少数族裔本科生研究人员接受了培训。这充分利用了布朗大学和图加卢学院（一所历史悠久的黑人学院或大学）之间50年的合作关系。公众外展工作旨在提高公众对科学、工程和技术概念的理解。这需要利用布朗大学成熟的科学漫画（sciitoons）计划创建两个新的sciitoons：“新兴太阳能电池技术”和“材料强度”。有令人信服的理由表明，卤化物钙钛矿材料具有迷人的、丰富的光-机械和机电耦合行为，但在这一领域的研究却极度缺乏。考虑到卤化物钙钛矿对新型太阳能电池和其他设备的前所未有的前景，有必要更深入地了解卤化物钙钛矿的机械降解，以及在设备中普遍存在的光学和/或电刺激。为了达到这个目的，这个项目来得正是时候，它包含了四个相互关联的任务，以及几个子任务。在任务1中，实验和定量研究了电场对卤化物钙钛矿单晶和薄膜断裂和裂纹愈合行为的影响。任务2涉及卤化物钙钛矿单晶塑性变形的定量研究，以及光的影响（光塑性）。在任务3中，研究了电场对卤化钙钛矿块状多晶球团蠕变随时间变化的影响。软卤化物钙钛矿中光载流子的高效生成和易离子迁移有望通过它们与卤化物钙钛矿中的点和线（位错）缺陷的相互作用介导裂纹愈合、塑性和蠕变现象。最后，在任务4中，以器件为例，展示了光塑性效应的表现。布朗大学开发的项目所需的大量研究基础设施得到充分利用。这项研究为下一代钙钛矿太阳能电池和其他更高效、更长期耐用的设备的开发提供了科学基础。因此，这项研究预计将具有很高的影响力，对研究人员和技术开发人员都很有用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical DescriptionSo-called ‘halide perovskites’ are a family of materials at the heart of a new type of solar-cell technology. These new solar cells are showing great promise as they are not only highly efficient in converting sunlight into electricity but also potentially very inexpensive to manufacture. However, the mechanical properties of these new solar cell materials are not known, especially under operating conditions of a solar cell: in sunlight, and also when electric current is passing through them. Thus, it is very important to study and understand these properties because they determine the long-term durability of the new solar cells, which are expected to operate efficiently for twenty years or more in the element. To that end, systematic research is conducted, where the following relevant mechanical properties of the new solar cell materials are studied under light and/or electric current: (1) cracking and healing of the cracks; (2) plastic deformation; and (3) time-dependent deformation. These studies are conducted on materials of well-defined chemical compositions, configurations, and morphologies. The results from these studies are analyzed critically to understand the behavior of the new solar cell materials. This is expected to have a broad impact on the ability to make highly durable, low-cost solar cells of the future, and to help this new solar-cell technology then reach its full potential. As part of this effort, underrepresented minority undergraduate researchers from Tugaloo College are trained. This leverages the fifty-year old partnership between Brown University and Tugaloo College -- an Historically Black College or University. The public outreach effort is aimed at enhancing the public's understanding of concepts in science, engineering, and technology. This entails leveraging the well-established science cartoons (SciToons) program at Brown University for creating two new SciToons on: ‘Emerging Solar Cells Technologies’ and ‘Strength of Materials.’Technical DescriptionThere are compelling reasons to suggest there are fascinating, rich opto-mechanical and electro-mechanical coupled behavior in halide perovskite materials, yet there is extreme paucity of research in this area. Considering the unprecedented promise of halide perovskites for new types of solar-cell and other devices, it is imperative to have a more in-depth understanding of the mechanical degradation of halide perovskites coupled with optical and/or electrical stimuli that are ubiquitous in devices. To that end, this project comes at a highly opportune time, and it entails four interrelated Tasks, and several Subtasks within. In Task 1, the effect of electric field on the fracture and crack-healing behavior in halide perovskite single-crystals and thin films is studied experimentally and quantified. Task 2 involves the quantitative study of plastic deformation of halide perovskite single-crystals, and the effect of light (photoplasticity). In Task 3, the effect of electric field on the time-dependent creep deformation of halide perovskite bulk polycrystalline pellets is studied. The efficient generation of photocarriers and facile ion migration in soft halide perovskites are expected to mediate crack-healing, plasticity, and creep phenomena, through their interactions with point and line (dislocations) defects in halide perovskites. Finally, in Task 4 the manifestation of photoplasticity effects, as an example, are demonstrated in devices. The considerable research infrastructure needed for the project developed at Brown University is leveraged fully. This research contributes to the scientific foundation for the development of next-generation perovskite solar-cell and other devices that are more efficient, and importantly more durable over the long term. As such, this research is expected to be highly impactful, and useful to researchers and technology developers alike.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.