Lead free organic-inorganic halide perovskite ferroelectrics with large piezoelectric responses

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Non-technical Description: Ferroelectricity describes the spontaneous electric response of certain materials to external electric field. Flexible ferroelectric thin films are attractive candidates for use in low-cost wearable sensors, energy conversion systems, and personal electronics. However, the current materials for this type of applications are ceramic, which are not sufficiently flexible and contain toxic lead element. Recently, a newly discovered, lead-free flexible organic-inorganic perovskite ferroelectric material show properties rivaling conventional rigid ceramic thin films. This project aims to explore the origin for the ferroelectric properties observed in this new organic-inorganic material and to design new materials of this type with improved properties. The project seeks to develop techniques for producing practical wearable and implantable ferroelectric devices using this newly-developed ferroelectric material. The integrative nature of theoretical investigation and experimental synthesis trains graduate and undergraduate students in cross-disciplinary skills that are essential for developing innovative solutions in the burgeoning field of wearable and implantable devices. Research results are expected to be available to the public via Ohio's Wright Center for Photovoltaics Innovation and Commercialization at The University of Toledo.Technical Description: The project includes both theoretical and experimental study of the mechanisms determining the large piezoelectric coefficient observed in organic-inorganic trimethylchloromethyl ammonium trichloromanganese (TMCM-TCM) perovskite, as well as development of synthesis methods for depositing high quality TMCM-TCM perovskite thin films. The theoretical study focuses on understanding how the TMCM molecules, the inorganic framework and the coupling between these two affect the ferroelectricity and piezoelectric coefficient of TMCM-TCM using density functional theory calculations. The theoretical study also includes searching for other molecules and inorganic octahedral frameworks that can form new organic-inorganic perovskite materials with enhanced ferroelectricity and piezoelectric coefficients. Additionally, the theoretical study provides understanding of the influence of point defects and lattice defects on the ferroelectric and piezoelectric properties. The experimental study focuses on developing synthesis processes including spin-coating, blade-coating and vacuum-thermal evaporation to deposit high quality organic-inorganic perovskite ferroelectric thin films. Characterization efforts, employing X-ray diffraction, scanning electron microcopy, UV-Vis spectroscopy, photoluminescence spectroscopy, and differential scanning calorimetry provide key assessments on the quality of the synthesized TMCM-TCM thin films. The experimental part also includes the investigation of the influence of various substrates on grain size, grain orientation, surface roughness, defect density, and uniformity of the synthesized TMCM-TCM thin films. If successful, the results provide pathways to realize efficient wearable and implantable ferroelectric and piezoelectric devices.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.