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

非技术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显示器和成像设备的应用。混合有机-无机卤化物钙钛矿是一类包含掺入有机分子的无机骨架的半导体。它们可以发展成为一类新的手性半导体，基于二维（2D）杂化有机-无机钙钛矿，通过将具有手性中心的大有机分子夹在无机单层之间。虽然这些2D手性钙钛矿是高度稳定的，但它们往往具有弱手性性质，空穴（正电荷载流子）和电子（负电荷载流子）之间的高结合能，以及低电荷迁移率，特别是平面外电荷迁移率，这极大地阻碍了它们在产生和检测偏振光中的应用。本计画将进行系统的基础研究，以揭示二维手性钙钛矿的结构与性质关系。研究小组通过引入手性n型（具有更多电子）和p型（具有更多空穴）半导体有机分子以及合理调整的无机单层组成，构建了新型2D手性钙钛矿结构。目标是制造在光下具有强手性性质、可调谐电子性质和上级电荷传输的2D钙钛矿。本研究的结果将进一步丰富手性半导体材料的基础知识。重要的是，该项目培训代表性不足的少数民族研究生和本科生研究人员。研究团队通过在康奈尔大学校园和伊萨卡科学中心举办的年度活动“拓展你的视野”，为年轻学生及其家人提供实践活动和演示，传播从这项工作中获得的知识。技术描述强手性，可调能带结构，和快速的电荷输运对于开发这类基于手性2D钙钛矿的手性半导体材料用于手电子是必不可少的。应用.本项目设计并合成了手性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货车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-和p-的化学结构来调节能带结构和能量取向。型半导体有机阳离子;和（3）增强电荷传输以允许电荷传输穿过有机-无机界面，从而降低激子结合能并增加面外电荷传输。三项研究任务正在进行中。任务1涉及手性n型和p型半导体有机阳离子的合成及其手性和电子性质的研究。在任务2中，我们合成了新型的n型和p型手性阳离子，并选择了无机亚晶格的组成来制备手性2D钙钛矿，并研究了它们的结构和手性光学性质。最后，在任务3中，手性2D钙钛矿的电子和手电子性质进行了彻底的研究。该研究推进了手性半导体材料的基础知识，包括手性晶相，有机和无机结构单元之间的手性转移，手性光学活性，电子能带结构，以及圆偏振光致发光和光电流。因此，这项研究不仅有望影响手电子学，还将影响自旋电子学、铁电子学和非线性光学领域。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。

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.