CAREER: Structural dynamics and optoelectronics of anharmonic soft semiconductors

金属卤化物钙钛矿是一类很有前途的材料，可用于太阳能电池和发光二极管等器件应用。它们卓越的电子性能与廉价的低温溶液处理相结合。考虑到在薄膜形成过程中或通过杂质引入缺陷，这种组合是令人惊讶的。这个CAREER项目的动机是需要更好地了解这些材料，并推进软半导体的科学和技术。理解卤化物钙钛矿特殊性质的关键在于它们的结构动力学，即组成材料的原子如何通过振动相互作用。与传统半导体不同，卤化物钙钛矿的结构动力学是非谐波的，是由软晶格中的长期和阻尼非线性相互作用引起的。本研究计划旨在建立软体半导体如何在极端晶格非调和性下运作的基本概念。PI将结合先进的光学和振动光谱学以及计算模型来研究这些材料。本研究的见解将有助于理解这些新兴材料的集体运动，并使其能够定制。这个项目的教育重点包括并利用了物理化学教学中计算的兴起。计算作为一种媒介和方法将被纳入教学、课程和课外项目以及学生研究中。PI还将探索科学数据的可视化和声音化，以架起科学与艺术的桥梁，将其带给学生和公众。本研究计划的重点是金属卤化物钙钛矿，这是一类相对较新的软半导体，具有强烈的非谐波结构动力学，与传统的准谐波半导体形成鲜明对比。在这个未知的领域，我们需要重新思考电子自由度和结构自由度是如何相互耦合的。我们的理解存在差距，需要基本的知识和新的概念来充分理解光电材料中软非调和晶格的起源、范围和后果。为了弥补这些差距，PI试图量化卤化物钙钛矿软半导体中普遍晶格非调和性及其对载流子弛豫的影响；卤化物钙钛矿软半导体铁弹性畴壁光电特性研究并发现新的二维和分子软半导体。该项目在多个时间和长度尺度上进行了相关的光谱研究。太赫兹频率晶格动力学将被探测并与光学范围、电子跃迁以及静态极限下的弹性特性相关联。重点将放在从金属卤化物钙钛矿中提取通用设计原则，并将这些见解推广到其他新兴材料。该项目由电子和光子材料计划和建立计划刺激竞争研究（EPSCoR）共同资助。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 DescriptionMetal halide perovskites are a promising class of materials with device applications such as solar cells and light-emitting diodes. Their exceptional electronic properties are coupled with inexpensive, low-temperature solution processing. This combination is surprising, given that defects can be introduced during film formation or through impurities. This CAREER project is motivated by the need to better understand these materials and to advance the science and technology of soft semiconductors. The key to understanding the exceptional properties of halide perovskites lies with their structural dynamics, that is, how atoms composing a material interact with one another through vibrations. Unlike conventional semiconductors, structural dynamics in halide perovskites are anharmonic, arising from long-ranged and damped nonlinear interactions in a soft lattice. This research project aims to establish fundamental concepts as to how soft semiconductors function with extreme lattice anharmonicity. The PI will investigate these materials with a combination of advanced optical and vibrational spectroscopy, coupled with computational modeling. Insights developed in this research will help to comprehend collective motions in these emerging materials and enable their customization. The educational focus of this project embraces and leverages the rise of computation for the teaching and learning of physical chemistry. Computation as a medium and approach will be incorporated into instruction, curricular and extracurricular projects, and student research. The PI will also explore the visualization and sonification of scientific data to bridge science and art, bringing this to students and the general public.Technical DescriptionThis research proposal focuses on metal halide perovskites, a relatively new class of soft semiconductors with strongly anharmonic structural dynamics in sharp contrast to conventional quasi-harmonic semiconductors. In this yet uncharted territory, we need to rethink how electronic and structural degrees of freedom couple with each other. Gaps in our understanding exist that call for basic knowledge and new concepts to fully appreciate the origin, extent, and consequence of a soft anharmonic lattice in optoelectronic materials. To bridge these gaps, the PI seeks to quantify universal lattice anharmonicity and its impact on charge carrier relaxation in halide perovskite soft semiconductors; characterize ferroelastic domain wall optoelectronics in halide perovskite soft semiconductors; and identify new two-dimensional and molecular soft semiconductors. The project features correlated spectroscopic investigations across multiple time and length scales. Terahertz frequency lattice dynamics will be probed and correlated to optical range electronic transitions as well as elastic properties in the static limit. Emphasis will be placed on distilling universal design principles from metal halide perovskites and generalizing these insights to other emerging materials.This project is jointly funded by the Electronic and Photonic Materials program and the Established Program toStimulate Competitive Research (EPSCoR).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.