Mechanisms of Triple Energy Transfer and Polaron Formation in Nanocrystals

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The Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division supports Professor Tianquan Lian and his group at Emory University to study energy transfer process and excited state lifetimes of nanomaterial systems critical to efficient and cost-effective solar energy conversion. This research is aimed at advancing two specific types of energy conversion technologies based on quantum dots (small semiconductor crystals). The first technology is photon upconversion. This process refers to converting two low energy packets of light (photons) into a higher energy photon, such as converting invisible infrared light to visible light. The second technology is the use of nanocrystals made from a specific category of materials called perovskites often used in solar cells. Unlike traditional solar cells, perovskite nanocrystals offer the possibility of tuning or adjusting the solar cell properties. This research may provide important guidance on the design and improvement of the energy conversion devices. Educational and broaden participation activities include the development of a new course on renewable energy and a demonstration module for the Atlanta Science Fair. With this award from the Macromolecular, Supramolecular, and Nanochemistry Program, Professor Lian’ group carries out the research with three specific aims. The first aim is to test the theoretical models of triplet energy transfer from quantum dots to molecular acceptors by examining its dependence on the electronic coupling strength and driving force using lead halide perovskite and cadmium chalcogenide quantum dots of different size and shell thickness. The second aim is to investigate the effect of exciton fine structure on triplet energy transfer rates from nanocrystals to molecular acceptors by examining their temperature dependence and to control these rates by changing the exciton fine structure through nanocrystal shapes. The third aim is to study the property of polarons (formation mechanism, size and energy) in low dimensional lead halide perovskite crystals, examining their dependences on the size, nanocrystal dimensionality, cations and solvent/ligand environment. The findings of this study can advance the understanding of triplet energy transfer from quantum dots to molecular acceptors and polaron formation in low dimensional perovskite nanocrystals. These advances, in turn, provide important guidance on the design and improvement of the energy conversion devices that are based on the abovementioned materials and processes.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.