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，因为其材料成本非常低，并且具有通过印刷制造的潜力，类似于印刷报纸或摄影胶片。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NSF材料研究部的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因素：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。Christians教授的研究重点是了解钙钛矿太阳能电池的特定已知故障模式，即中心材料晶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及其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预计将作为指导，使研究人员能够准确地理解，量化和减轻这种故障模式在太阳能电池长达数年的户外运行中的影响。该项目还包括由基督徒教授在霍普学院开展的辅导活动，霍普学院主要是一所本科院校。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机会，以建立他们的技能作为研究科学家，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计划ExploreHope合作开展的工作，为传统上代表性不足的当地高中生设计和实施一个名为“Digging into Photoelectronics”的夏季STEM研究夏令营，让这些学生体验太阳能电池和STEM研究。技术概述材料的晶相是其化学、物理和电子特性中最重要的方面之一。卤化物钙钛矿，钙钛矿太阳能电池中的吸收材料，具有角共享金属卤化物八面体，但可以转化为其他晶相，其中这些八面体倾斜以成为面共享或边共享。该项目由NSF材料研究部的固态和材料化学计划支持，促进了对从钙钛矿相到非钙钛矿相的相变的理解，这对于设计卤化物钙钛矿吸收剂非常重要，这些吸收剂在长达数年的户外操作中保持稳定的钙钛矿相。非钙钛矿相的形成对材料成分和晶体尺寸敏感，但这些参数还没有得到很好的理解。Christians实验跟踪，诱导和研究卤化物钙钛矿材料的相变到其竞争的非钙钛矿相。该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，在引发和催化非钙钛矿相形成中的作用。综上所述，该项目推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、改进的器件设计和更好的加速器件寿命协议方面发挥作用。该奖项反映了NSF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.