RUI: Exploring Nonperovskite Phase Growth Mechanisms in Halide Perovskites

低成本太阳能电池技术的发展对于减少能源部门的污染以及替代发电的成本至关重要。实现这一目标的最佳技术可能是所谓的钙钛矿太阳能电池，因为它的材料成本非常低，而且有可能通过印刷制造，类似于报纸或摄影胶片的印刷。在实验室条件下，钙钛矿太阳能电池显示出与目前市售太阳能电池相当的性能。该项目由美国国家科学基金会材料研究部固态和材料化学项目支持，解决了该技术在基础材料化学水平上的一个主要未知问题：钙钛矿薄膜在现实条件下的长期耐久性。为了加快耐久性研究——在六个月内了解太阳能电池是否能存活30年——有必要能够理解和预测材料系统的各种失效模式。christian教授的研究重点是了解钙钛矿太阳能电池的特定已知失效模式，即中心材料晶体相或结构的变化导致太阳能电池性能下降。钙钛矿材料的各个方面都经过仔细调整，以获得对其降解条件和特定失效模式的预测性理解。从这项研究中获得的理解水平有望作为指导，使研究人员能够准确地理解，量化和减轻这种失效模式在太阳能电池长达数年的户外运行中的影响。该项目还包括由霍普学院（Hope College）的christian教授进行的指导活动。它允许本科生参与尖端材料研究，并为这些学生提供了一个培养研究科学家技能的机会，并在国家研究会议上展示他们的工作。该奖项还将支持与校园外展项目explorerhope一起完成的工作，设计和实施一个名为“深入光伏”的暑期STEM研究营，为传统上代表性不足的当地高中生提供太阳能电池和STEM研究的经验。材料的结晶相是决定其化学、物理和电子性能的最重要的方面之一。卤化物钙钛矿，钙钛矿太阳能电池中的吸收材料，具有共享角的金属卤化物八面体，但可以转化为其他晶体相，这些八面体倾斜成为面或边共享。该项目由美国国家科学基金会材料研究部固态和材料化学项目支持，促进了对钙钛矿相到非钙钛矿相相变的理解，这对于设计在长达数年的户外运行中保持钙钛矿相稳定的卤化物钙钛矿吸收剂非常重要。非钙钛矿相的形成对材料成分和晶体尺寸很敏感，但这些参数还没有得到很好的理解。christian教授通过实验跟踪、诱导和研究了卤化物钙钛矿材料向非钙钛矿相的相变。项目的第一阶段揭示了这一过程的能量学、速率和机制。基于这些发现，研究人员随后探索了卤化物钙钛矿材料的组成和形态变化如何影响这些参数。这项工作揭示了外部刺激，如湿度，在启动和催化非钙钛矿相形成中所起的作用。总而言之，该项目促进了对卤化物钙钛矿相稳定性和相变的理解，从而将在研究界寻找更稳定的材料、改进的设备设计和更好的加速设备寿命协议中发挥作用。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。

Non-Technical SummaryThe development of lower cost solar cell technologies is crucial for reducing pollution from the energy sector as well as the cost of alternative electricity generation. The technology to best achieve this goal might be so-called perovskite solar cells because of very low material costs and the potential for manufacturing by printing, similar to the printing of newspaper or photographic film. Under laboratory conditions perovskite solar cells show performances on par with current commercially available solar cells. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, addresses a major unknown for the technology at a fundamental materials chemistry level: long-term durability of perovskite films under real-world conditions. To speed up durability studies - to learn in six months if the solar cells will survive 30 years - it is necessary to be able to understand and predict the various failure modes of the materials system. Prof. Christians’ research focuses on understanding a specific known failure mode of perovskite solar cells, a change in the central material’s crystalline phase or structure leading to a decrease in solar cell performance. Various aspects of the perovskite materials are carefully adjusted to gain a predictive understanding of the conditions under which they degrade and their specific failure mode. The level of understanding gained from this research is expected to serve as a guide to allow researchers to accurately understand, quantify and mitigate the effects of this failure mode during years-long outdoor operation of solar cells. This project also includes mentoring activities undertaken by Prof. Christians at Hope College, a primarily undergraduate institution. It allows undergraduate students to participate in cutting-edge materials research and provides an opportunity for these students to build their skills as research scientists and to present their work at national research conferences. This award will also support work done in tandem with ExploreHope, a campus outreach program, to design and implement a summer STEM research camp, called "Digging into Photovoltaics", for traditionally underrepresented local high school students to give these students experience with solar cells and STEM research.Technical SummaryA material's crystalline phase is one of the most important aspects of its chemical, physical, and electronic properties. Halide perovskites, the absorber material in perovskite solar cells, have corner-sharing metal halide octahedra, but can transform into other crystal phases where these octahedra tilt to become face- or edge-sharing. This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, advances the understanding of the phase transformation from perovskite phases to nonperovskite phases which is important to designing halide perovskite absorbers that remain stable in their perovskite phase during years-long outdoor operation. Nonperovskite phase formation is sensitive to material composition and crystal size, but these parameters are not well understood. Prof. Christians experimentally tracks, induces and studies the phase transformations of halide perovskites materials into their competing nonperovskite phases. The first phase of the project uncovers the energetics, rate, and mechanism of this process. Based on these findings the researchers then explore how compositional and morphological changes to the halide perovskite materials influence these parameters. This work sheds light on the role that external stimuli, such as humidity, play in initiating and catalyzing nonperovskite phase formation. Taken together, this project advances the understanding of halide perovskite phase stability and phase change and will thereby play a role in the research community's search for more stable materials, improved device designs, and better informed accelerated device lifetime protocols.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.