CAREER: Nanostructural strain to control stability and function in halide perovskites

非技术摘要这个NSF职业奖项由材料研究部的固态和材料化学计划支持，通过使亚稳态结构变得稳定，从根本上扩大了可用于太阳能电池和其他应用的材料调色板。亚稳态结构只是暂时存在，然后才会恢复到它们“首选”的稳定结构。尽管存在这一缺点，但仍然存在大量具有其他理想性能的亚稳态材料，用于各种技术应用。例如，在被称为金属卤化物钙钛矿的各种材料中，已知亚稳定变体将高效太阳能电池(超过23%的太阳能到电能转换效率)的理想性能与极低成本和可扩展的合成相结合。该项目为在以前没有以稳定形式准备的结构中利用这种理想行为提供了关键的新途径。Aaron Fafarman的研究小组采用的实现这些结构稳定的新技术依赖于使非常小的-人类头发厚度的万分之一-亚稳定材料的能力，从而控制在结构中诱导应变。这使得有选择地增强它们的稳定性成为可能。利用这项工作中确立的基本原则可以产生的低成本太阳能电池的巨大社会红利包括减少温室气体排放、增强国内能源安全、可持续的能源经济以及在开发和制造一种重要的高科技商品方面增加就业机会。此外，通过该项目，本科生和研究生将接受化学、固态物理和电气工程工具和概念方面的跨学科培训，掌握21世纪制造业经济所需的技能。此外，作为这项工作的一部分，地方公立初中学生将获得实践经验，以一种旨在增强他们对STEM领域兴趣的形式合成太阳能转换材料。技术摘要：这个由材料研究部固态和材料化学项目支持的NSF职业奖项目，开发了近环境温度化学和物理方法，通过了解和控制纳米级的晶格应变来合成和稳定非平衡半导体离子晶体。通过定义纳米应变，这项研究为将卤化物钙钛矿合成复杂的、远离平衡的功能材料提供了全新的途径-这些途径可能被证明可推广到更广泛的离子固体类别。通过引入降维(纳米结构)、施加负压和诱导空间定义的应变扰动三种方法测试了应变与组成稳定性、钙钛矿相稳定性和功能性质的相关性。由于嵌入在具有较小热膨胀系数的第二材料中的材料的受挫热收缩，在通用方案中实现了负压。通过单独的纳米结构和工程热应力，可以稳定低密度和高对称性的晶型，而这些晶型在整体上是无法获得的。在一个相关的概念中，空间定义的应变微扰被用作一种手段来修正掺杂离子晶体中杂质离子的初始分布。由此产生的空间工程组成梯度可以用于各种功能目的；它们还包括用于探测应变-结构-函数关系的工具。利用这项工作中确立的基本原则可能产生的低成本太阳能电池的巨大社会红利包括减少温室气体的人为排放、提高国内能源安全和可持续能源经济。此外，通过该项目，本科生和研究生将接受化学、固态物理和电气工程工具和概念方面的跨学科培训，掌握21世纪制造业经济所需的技能。此外，作为这项工作的一部分，当地的公立初中学生将获得实践经验，以增强他们对STEM领域的兴趣。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstractThis NSF CAREER award, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, fundamentally expands the palette of materials available for solar cells and other applications by rendering metastable structures stable. Metastable structures exist only temporarily before reverting to their "preferred" stable structure. In spite of this drawback there exist a vast number of metastable materials with otherwise ideal properties for a variety of technological applications. For example, among the diverse class of materials known as metal halide perovskites metastable variants are known that combine ideal properties for efficient solar cells (over 23% efficient solar-to-electricity energy conversion) with extremely low-cost and scalable synthesis. This project provides critical new avenues to exploiting such ideal behaviors in structures that have not been prepared in stable forms before. The novel techniques employed in Aaron Fafarman's research group to achieve the stabilization of these structures relies on the ability to make very small - one ten-thousandths of the thickness of a human hair - metastable materials and thereby with control induce strain in the structures. This makes it possible to selectively enhance their stability. The tremendous social dividends of the low-cost solar cells that could result from utilizing the fundamental principles established in this work include reduced emission of green-house gases, increased domestic energy security, a sustainable energy economy and growth of jobs in the development and manufacture of an important high-tech commodity. Additionally, through this project, undergraduate and graduate students receive interdisciplinary training in chemistry, solid-state physics and electrical engineering tools and concepts, emerging with skills for a twenty first century manufacturing economy. Also, as part of this work, local, public junior high students get hands-on experience synthesizing solar energy conversion materials in a format designed to bolster their interest in the STEM field. Technical abstract:This NSF CAREER award project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research, develops near-ambient-temperature chemical and physical approaches to synthesize and stabilize non-equilibrium semiconducting ionic crystals by understanding and controlling lattice strain with nanoscale precision. Through defined nanostrain, this research provides entirely novel avenues for the synthesis of halide perovskites into complex, far-from-equilibrium, functional materials - avenues that may prove generalizable to a much wider class of ionic solids. The correlations between strain and compositional stability, perovskite phase-stability and functional properties are tested in three ways: by imparting reduced dimensionality (nanostructuring), applying negative pressure and inducing spatially defined-strain perturbations. Negative pressure is achieved in a versatile scheme due to frustrated thermal contraction of a material embedded in a second material with a smaller thermal expansion coefficient. Both by nanostructuring alone and by engineered thermal stresses, low density and high symmetry crystal polymorphs are stabilized that are inaccessible in the bulk. In a related concept, spatially defined-strain perturbations are utilized as a means to modify the as-made distribution of impurity ions in doped ionic crystals. The resulting spatially engineered composition gradients can be harnessed for a variety of functional purposes; they also comprise a tool for probing the strain-structure-function relationship. The tremendous social dividends of the low-cost solar cells that could result from utilizing the fundamental principles established in this work include reduced anthropogenic emission of green-house gases, increased domestic energy security, and a sustainable energy economy. Additionally, through this project, undergraduate and graduate students receive interdisciplinary training in chemistry, solid-state physics and electrical engineering tools and concepts, emerging with skills for a twenty first century manufacturing economy. Also, as part of this work, local, public junior high students get hands-on experience synthesizing solar energy conversion materials in a format designed to bolster their interest in the STEM field.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.