NSF/DMR-BSF: Multiscale-Modeling and Raman Spectroscopy to Uncover Correlated Atomic Motions in Hybrid and Halide Perovskites

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NONTECHNICAL SUMMARYThe National Science Foundation and the United States -- Israel Binational Science Foundation (BSF) jointly support this collaboration between a US-based researcher and an Israel-based researcher. The NSF Division of Materials Research funds this award, which supports research and education on how materials absorb light, how electrons behave after absorbing that energy, and how ionic motions can influence them. Many important processes involve interactions of light with matter, including solar energy conversion, light detection, and optical computing. This project brings together theoretical and experimental efforts to explore these processes using state-of-the-art investigational techniques. The PI and his group plan to focus on hybrid perovskites, materials that have recently been shown to have promising photovoltaic properties. Despite this promise, the lack of physical understanding of the ability of these materials to convert light to electricity impedes further progress. The theoretical work includes quantum mechanical modeling of materials and simulations, aiming to provide a deep understanding of the electronic states in these materials, as well as an understanding of the vibrational properties. The experimental work will center around using light to excite vibrational motions, revealing how the ions move, and how the ionic motions are affected by temperature, electric field, and previous light excitation. These spectroscopic studies of the vibrations will be connected to the theory and modeling to produce a complete picture of the behavior of these materials. The advancement of highly efficient photovoltaics that are easy to fabricate is a compelling societal need. The hybrid perovskites appear to be moving toward commercial acceptance, except that the basic physics behind their favorable properties and their evolution and degradation are not understood. This project represents an opportunity for theoretical condensed matter physics to play a vital role in assessing material properties and in opening the gateway to widespread acceptance of this technology. This could provide a wide range of societal dividends from improved and less expensive photovoltaics to sensors and optical computing elements.This project also offers unique opportunities for engaging and training the next generation of scientists to apply complex condensed-matter physics in a context of compelling interest to them, through venues ranging from public lectures, in-class discussions and tailored modules, to research projects at the undergraduate, graduate, and postdoctoral levels, and binational and international conferences. The US-based graduate students will travel to Israel to carry out research at the Israeli PI's group.TECHNICAL SUMMARY The National Science Foundation and the United States -- Israel Binational Science Foundation (BSF) jointly support this collaboration between a US-based researcher and an Israel-based researcher. The NSF Division of Materials Research funds this award, which supports research and education on uncovering and understanding the correlated ionic motions in halide (and hybrid organic-inorganic) perovskite (HOIP) materials. This class of materials has shown enormous potential as next-generation photovoltaic materials. Despite this promise, the lack of physical understanding of the ability of these materials to convert light to electricity impedes further progress. Ionic motion plays a key role in the property evolution of these materials, and it has been proposed to play a signature role in the anomalously favorable excited-carrier dynamics and lifetime.The PIs propose theoretical modeling and targeted Raman spectroscopy to reveal and rationalize a range of ionic motions, including harmonic and anharmonic phonons, incipient polar order, and other correlated ionic motions on various length- and time-scales. First-principles calculations will provide insight into interatomic interactions and short-time dynamical features. Longer time scales will be accessed via molecular dynamics and will be analyzed with a suite of correlation function tools. Raman spectroscopy will probe ionic motions and confirm and extend theoretical interpretations. Specific activities include: i) revealing and analyzing correlated ionic motions and the onset of polar order in the hybrid and halide perovskites; ii) the effect of temperature and electric field on dynamic and static ordering; iii) hydrogen bonding and structural ordering; iv) illumination-induced structural ordering and disordering; v) polar ordering and the Rashba effect.The advancement of highly efficient photovoltaics that are easy to fabricate is a compelling societal need. The hybrid perovskites appear to be moving toward commercial acceptance, except that the basic physics behind their favorable properties and their evolution and degradation are not understood. This project represents an opportunity for theoretical condensed matter physics to play a vital role in assessing material properties and opening the gateway to widespread acceptance of this technology. This project will make connections between disparate scientific disciplines including crystalline solids, liquids, and molecular materials, and will develop new techniques for Raman spectroscopic interrogation of materials and correlation function theoretical analysis of complex ionic behaviors.This project also offers unique opportunities for engaging and training the next generation of scientists to apply complex condensed-matter physics in a context of compelling interest to them, through venues ranging from public lectures, in-class discussions and tailored modules, to research projects at the undergraduate, graduate, and postdoctoral levels, and binational and international conferences. The US-based graduate students will travel to Israel to carry out research at the Israeli PI's group.