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

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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.