Understanding and Enhancing Electronic Coupling Between Metal Halide Perovskite Quantum Dots Through Surface Molecular Engineering

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Nanoparticles are extremely small crystals. They can be just a few nanometers in size, or about 100,000 thinner than a sheet of paper, and they can be formed from many different types of materials, including semiconductors. When the electrons are squeezed into very small semiconductor nanocrystals, they become quantum-confined and new properties emerge, which can be harnessed for use in new technologies. Before proceeding to applications, researchers must learn how to pack the quantum dots (QDs) together into solids so that one nanoparticle can share its electrons with another. With support from the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professors Jin Z. Zhang and Yuan Ping from University of California Santa Cruz (UCSC) are studying QD solids formed from a new class of semiconductors called perovskites. Unlike traditional semiconductors, such as silicon, perovskites are a mixture of inorganic components and organic molecules and this gives rise to unusual properties. Working with their students, Professors Zhang and Pin are developing ways to create stable QD solids where the electrons are easily shared. Their discoveries could impact applications ranging from quantum computing to solar cells. The project also provides training opportunities for future scientists in advanced experimental and computational techniques. Through their "The Sun, Spectroscopy, and Santa Cruz" events held each summer, the research groups are introducing the project to local high school students and teachers to enhance public awareness about science. The research team is developing novel semiconductor QD solids based on metal halide (MH) perovskites. This research addressws the challenge that charge transport properties of QD solids are often limited due to weak coupling between QDs, hindering device applications in emerging technologies. The project is systematically studying the fundamental factors, such as size, shape and surface, that determine the electronic coupling between perovskite QDs (PQDs) by developing designer ligands that enhance both the coupling between the PQDs and their stability. The coupling between PDQs and interaction between ligands are characterized using a combination of time-resolved photoluminescence, transmission electron microscopy, infrared spectroscopy, and ultrafast pump-probe methods. Unique conductive or aromatic ligand molecules are expected to both stabilize the QDs and enhance their electronic coupling so that the QD solids will exhibit strong charge transport while maintaining the novel properties of the QDs. Computational studies based on state-of-the-art quantum mechanical methods are exploring the ligand-PQD interaction and inter-PQD coupling to guide and corroborate experimental studies.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.