Enhance Exciton Transport in Perovskite Quantum Dot Solids through Coherent Interactions

这个项目使用超快激光在被称为量子点的微小半导体纳米粒子之间制造光能的“电影”。这些量子点是有效的光吸收剂，对太阳能电池或发光二极管等设备有潜在的用处。在设备中，量子点必须紧密地排列在一起，以促进能量从一个量子点转移到下一个量子点。因此，量子点之间的距离和能量迁移的速度对器件效率有很大的影响。通过成像能量如何在不同包装的量子点固体中移动，本研究旨在通过控制能量迁移率为设计有效光能收集的结构提供指导。为了实现这些目标，研究人员开发了合成策略来控制量子点的大小和用于连接它们的化学连接剂。然后，这些量子点被用作“人造原子”，并组装成有序的超晶格结构。研究小组还开发了显微镜技术，以10飞秒（1飞秒是1千万亿分之一秒）的分辨率记录快速能量转移事件，并以50纳米（1纳米是10亿分之一米）的分辨率成像能量迁移距离。研究和教育活动被整合在一起，通过K-12、本科和研究生的科学教育来教育下一代太阳能研究人员。pi与Science Express和普渡大学的AP Fridays合作，让K-12学生参与到尖端的实验室环境中。这个项目的成果被用来利用播客和视频媒体向公众宣传新的太阳能技术。胶体量子点固体中的远程激子输运和相干性在其光电和量子信息应用中是非常理想的。然而，由于与这些系统中的电子耦合强度相比，胶体量子点固体中的激子输运相对较大，因此到目前为止，激子输运几乎完全是在非相干状态下实现的，激子局限于单个量子点。局域激子的非相干输运是获得远程相干输运的主要限制。在这个项目中，钙钛矿量子点之间的强偶极子-偶极子相互作用被利用来通过促进离域激子的相干运动来增强输运。该团队通过使用超快相干显微镜阐明了传输机制，该显微镜具有~10 fs的时间分辨率和优于50 nm的空间分辨率。激子传播距离、离域长度和相干输运贡献作为温度的函数来测量。激子离域的程度系统地通过改变粒子间距离、电子耦合和使用配体化学的维数来控制。该项目为使用钙钛矿量子点作为构建块设计激子材料提供了指导方针。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。

This project uses ultrafast lasers to make “movies” of light energy traveling between tiny semiconductor nanoparticles known as quantum dots. These quantum dots are efficient light absorbers and potentially useful for devices such as solar cells or light emitting diodes. In a device, quantum dots must be closely packed together in order to facilitate energy transfer from one quantum dot to the next. As a result, the distance between quantum dots and the speed at which energy migrates has a strong effect on device efficiency. By imaging how energy moves in quantum dot solids with different packings, this research aims to provide guidelines for designing structures for efficient light energy harvesting through control of energy migration rates. To achieve these goals, synthetic strategies are developed to control the size of the quantum dots and the chemical linkers used to connect them. Then, these quantum dots are used as “artificial atoms” and assembled into well-ordered structures known as superlattices. The research team also develops microscopy techniques to record fast energy transfer events with a resolution of 10 femtoseconds (a femtosecond is one quadrillionth of a second) and to image energy migration distances with a resolution of 50 nanometers (a nanometer is one billionth of a meter). The research and educational activities are integrated to educate the next generation of solar energy researchers through K-12, undergraduate, and graduate science education. The PIs partner with Science Express and AP Fridays at Purdue to involve K-12 students in a cutting-edge laboratory environment. Results from this project are utilized to educate the general public on new solar energy technologies using podcast and video media.Long-range exciton transport and coherence in colloidal quantum dot solids are highly desirable for their optoelectronic and quantum information applications. However, exciton transport in colloidal quantum dot solids thus far has been almost exclusively realized in the incoherent regime with excitons localized in individual quantum dots due to the relatively large energetic disorder compared to the electronic coupling strength in these systems. Incoherent transport of localized excitons presents a major limitation in obtaining long-range coherence and transport. In this project, strong dipole-dipole interactions between perovskite quantum dots are leveraged to enhance transport by promoting coherent motion of delocalized excitons. The team elucidates transport mechanisms by employing ultrafast coherent microscopy with ~10 fs time resolution and better than 50 nm spatial resolution. Exciton propagation distance, delocalization length, and coherent transport contributions are measured as a function of temperature. The extent of exciton delocalization is systematically controlled by varying inter-particle distance, electronic coupling, and dimensionality using ligand chemistry. The project provides guidelines for designing excitonic materials using perovskite quantum dots as building blocks.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.