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

非技术摘要这个NSF CAREER奖，由材料研究部的固态和材料化学计划支持，通过使亚稳态结构稳定，从根本上扩展了太阳能电池和其他应用的材料。亚稳结构在恢复到它们的“优选”稳定结构之前仅暂时存在。尽管有这个缺点，但存在大量的亚稳态材料，它们具有用于各种技术应用的理想性质。例如，在被称为金属卤化物钙钛矿的多种材料中，已知亚稳态变体将高效太阳能电池的理想性能（超过23%的太阳能-电能转换效率）与极低的成本结合起来。和可扩展的合成。联合收割机。该项目提供了重要的新途径，以利用这种理想的行为，在结构中，还没有准备在稳定的形式之前。Aaron Fafarman的研究小组采用的新技术来实现这些结构的稳定性，依赖于制造非常小的能力-人类头发厚度的万分之一-亚稳态材料，从而在结构中控制诱导应变。这使得有可能选择性地增强它们的稳定性。利用这项工作中确立的基本原则，低成本太阳能电池可产生巨大的社会红利，包括减少温室气体排放、提高国内能源安全、可持续能源经济以及增加开发和制造一种重要的高科技商品的就业机会。此外，通过该项目，本科生和研究生接受化学，固态物理和电气工程工具和概念的跨学科培训，为二十一世纪世纪制造业经济提供技能。此外，作为这项工作的一部分，当地的公立初中学生获得了合成太阳能转换材料的实践经验，这种合成材料的形式旨在提高他们对STEM领域的兴趣。 这个NSF CAREER奖项目由材料研究部的固态和材料化学项目支持，开发了近环境温度的化学和物理方法，通过理解和控制纳米级精度的晶格应变来合成和稳定非平衡半导体离子晶体。通过定义的纳米应变，这项研究为将卤化物钙钛矿合成为复杂的，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。应变和组成稳定性，钙钛矿相稳定性和功能特性之间的相关性进行了测试，在三种方式：通过赋予减少的维度（纳米结构），施加负压和诱导空间定义的应变扰动。由于嵌入具有较小热膨胀系数的第二材料中的材料的受抑热收缩，在通用方案中实现负压。通过单独的纳米结构化和通过设计的热应力，低密度和高对称性晶体多晶型物被稳定，这在本体中是不可接近的。在一个相关的概念中，利用空间限定的应变扰动作为一种手段，以修改掺杂的离子晶体中的杂质离子的分布。由此产生的空间工程组成梯度可以利用各种功能的目的，它们也包括一个工具，用于探测应变-结构-功能的关系。低成本太阳能电池的巨大社会红利可能来自于利用这项工作中建立的基本原则，包括减少温室气体的人为排放，增加国内能源安全和可持续的能源经济。此外，通过该项目，本科生和研究生接受化学，固态物理和电气工程工具和概念的跨学科培训，为二十一世纪世纪制造业经济提供技能。此外，作为这项工作的一部分，当地公立初中学生获得了合成太阳能转换材料的实践经验，旨在提高他们对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 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.