Collaborative Research: Amorphous-Crystalline Switching in Organic-Inorganic Hybrid Semiconductors

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Nontechnical Description: Hybrid organic-inorganic perovskite (HOIP) semiconductors represent an emerging materials class that offers a unique opportunity to combine and individually tailor desirable characteristics from organic and inorganic systems within a single molecular-scale composite, and such systems already provide outstanding properties for next generation solar cells, light-emitting devices, and photodetectors. Current HOIP research generally focuses on the crystalline state, in which constituent atoms repeat in a periodic and well-ordered fashion. With this project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, Prof. David Mitzi at Duke University and Prof. Michael Toney at the University of Colorado and their research groups will investigate methods to extend beyond the current state-of-the-art in HOIPs to demonstrate and understand how controllable disorder can be introduced within HOIPs through an accessible melt and glass state, and how this disorder can be employed to significantly expand the range of properties for the HOIP family. Such research targets creation of design rules to guide future development of meltable and glass forming HOIPs and to understand how properties of the glass and melt states differ from the crystalline state. Reversible switching between crystalline and glass states, employing small changes in temperature, vastly broadens the prospective application space for HOIPs to include low-power phase-change memory, neuromorphic computing, advanced sensing, and reconfigurable photonics. The research closely connects with education and outreach. Involved undergraduate, graduate and postdoctoral researchers engage with the national labs for structure-property studies, and this experience gets conveyed to the broader student body through an on-going student-oriented energy materials seminar series. Structure-property data for the glasses are made broadly available to the community through a perovskite-focused database, representing the first collection of HOIP glass state data. Project research connects to traditionally underserved STEM communities through an NSF REU, "Nanoscale Detectives -- Elucidating the Structure and Dynamics of Hybrid Perovskite Systems," and through a Pre-Collegiate Development Program that prepares first generation/low-income students from inner-city and rural areas.Technical Description: This project, supported by the Solid State and Materials Chemistry program in the Division of Materials Research at NSF, combines targeted synthesis, with detailed structure and property characterization for a new class of hybrid organic-inorganic perovskite (HOIP) semiconductors that offers facile access to melt and glassy states, focusing on two key directions. First, the project uses targeted HOIP synthesis using developed design rules for low HOIP melting temperature and prospective glass-crystalline switching, seeking to broaden the family of HOIPs that can effectively access melt/glass states. Successfully created materials are structurally characterized using X-ray/neutron scattering techniques, coupled with extended X-ray absorption fine structure, Raman spectroscopy and rheometry. This intensive characterization captures the extended crystalline and local melt/glass state structures, as well as underlying mechanical properties. Second, while HOIP crystalline state properties are broadly studied and understood, the current project connects HOIP melt and glass local structure with corresponding thermal and optoelectronic properties, studied using differential scanning calorimetry and various optical spectroscopies, targeting a pathway for enhancing and tuning these properties. By exploring fundamental structure-property connections associated with the HOIP melt and glass states, the research seeks to ultimately create a pathway for predictably designing HOIPs with targeted glass and melt state properties, as is increasingly already possible for the crystalline state.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.