Two-Dimensional Chiral Perovskites with Tunable Electronic Band Structure and Superior Charge Transport

非技术性描述手性材料具有不可重叠的结构和镜像。手性半导体具有诸如产生和检测偏振光以及制造3D显示器和成像设备等应用。杂化有机-无机卤化物钙钛矿是一类包含有机分子的无机框架的半导体。通过将具有手性中心的大型有机分子夹在无机单层之间，它们可以发展成为基于二维（2D）杂化有机-无机钙钛矿的新型手性半导体。虽然这些2D手性钙钛矿具有很高的稳定性，但它们往往具有较弱的手性，空穴（正电荷载流子）与电子（负电荷载流子）之间的结合能较高，电荷迁移率尤其是面外电荷迁移率较低，这极大地阻碍了它们在偏振光产生和检测方面的应用。本项目将开展系统的基础研究，揭示二维手性钙钛矿的结构-性能关系。研究小组通过结合手性n型（具有更多电子）和p型（具有更多空穴）半导体有机分子和合理调整无机单层组成，构建了新的二维手性钙钛矿结构。目标是制造具有强光手性、可调谐电子特性和优越电荷输运的二维钙钛矿。这项研究的结果将推进手性半导体材料的基础知识。重要的是，该项目培养未被充分代表的少数民族研究生和本科生研究人员。研究团队通过每年在康奈尔大学校园和伊萨卡科学中心举办的“拓展你的视野”活动，为年轻学生和他们的家人提供实践活动和示范，传播从这项工作中获得的知识。技术描述强手性，可调谐的能带结构和快速电荷传输对于开发这种基于手性2D钙钛矿的新型手性半导体材料至关重要，用于手电子应用。本项目设计和合成了手性n型和p型半导体有机阳离子，以取代传统的非导电有机阳离子，以允许(1)通过增强有机阳离子与无机亚晶格之间的氢键相互作用和范德华相互作用来增加手性；(2)通过改变无机亚晶格的组成和n型和p型半导体有机阳离子的化学结构来调整能带结构和能量排列；(3)增强电荷输运，允许电荷通过有机-无机界面输运，从而降低激子结合能，增加面外电荷输运。进行了三项研究任务。任务1包括手性n型和p型半导体有机阳离子的合成以及它们的手性和电子性质的研究。在任务2中，利用合成的新型n型和p型手性阳离子和选择的无机亚晶格组成制备了手性二维钙钛矿，并研究其结构和手性性质。最后，在任务3中，深入研究了手性二维钙钛矿的电子和手端电子性质。这项研究提高了手性半导体材料的基础知识，包括手性晶体相、有机和无机构建块之间的手性转移、手性活性、电子带结构、圆极化光致发光和光电流。因此，本研究不仅会对手旋电子学产生影响，还会对自旋电子学、铁电子学和非线性光学等领域产生影响。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 DescriptionChiral materials have non-superimposable structures and mirror images. Chiral semiconductors have applications such as generating and detecting polarized light and making 3D displays and imaging devices. Hybrid organic-inorganic halide perovskites are a family of semiconductors that contain inorganic frameworks incorporating organic molecules. They can be developed into a new class of chiral semiconductors based on two-dimensional (2D) hybrid organic-inorganic perovskites by incorporating large organic molecules with a chiral center sandwiched between inorganic single layers. While these 2D chiral perovskites are highly stable, they tend to have weak chiral properties, high binding energy between holes (positive charge carriers) and electrons (negative charge carriers), and low charge mobility, especially out-of-plane charge mobility, which greatly hinders their applications in generating and detecting polarized light. This project will conduct systematic fundamental studies to reveal the structure-property relationship of 2D chiral perovskites. The research team constructs novel 2D chiral perovskite structures by incorporating chiral n-type (having more electrons) and p-type (having more holes) semiconducting organic molecules and rationally tuned compositions of inorganic single layers. The goal is to fabricate 2D perovskites with strong chiral properties under light, tunable electronic properties, and superior charge transport. The results from this research will advance fundamental knowledge of chiral semiconducting materials. Importantly, this project trains underrepresented minority graduate and undergraduate researchers. The research team disseminates the knowledge gained from this work by providing hands-on activities and demonstrations for young students and their families through the annual event of Expanding Your Horizons at Cornell campus and Ithaca Sciencenter.Technical DescriptionStrong chirality, tunable band structure, and fast charge transport are essential for developing this new class of chiral semiconducting materials based on chiral 2D perovskites for chiroptoelectronic applications. This project designs and synthesizes chiral n- and p-type semiconducting organic cations to replace conventional non-conducting organic cations to allow (1) increasing the chirality by enhancing hydrogen bonding interactions and van der Waals interactions between organic cations and inorganic sublattices; (2) tuning band structure and energy alignment via varying the composition of inorganic sublattice and chemical structures of n- and p-type semiconducting organic cations; and (3) enhancing charge transport to allow charge transport across the organic-inorganic interfaces to reduce exciton binding energy and increase out-of-plane charge transport. Three research tasks are pursued. Task 1 involves the synthesis of chiral n- and p-type semiconducting organic cations and the investigation of their chiral and electronic properties. In Task 2, synthesized novel n- and p-type chiral cations and selected composition of inorganic sublattice are used to fabricate chiral 2D perovskites and their structural and chiroptical properties are studied. Finally, in Task 3 the electronic and chiroptoelectronic properties of chiral 2D perovskites are thoroughly investigated. This research advances fundamental knowledge of chiral semiconducting materials including chiral crystalline phases, chirality transfer between organic and inorganic building blocks, chiroptical activity, electron band structure, and circularly polarized photoluminescence and photocurrent. Therefore, this research is expected to impact not only chiroptoelectronics but also the fields of spintronics, ferroelectronics, and non-linear optics.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.