New Low-Temperature Synthetic Routes to Functional Perovskite and Semiconductor Nanocrystals

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)TECHNICAL SUMMARY:The goal of this research program is to develop rational synthetic methods for the low temperature, solution phase synthesis of functional inorganic nanocrystals for energy applications. Lower temperature reactions are energy efficient and offer the added benefit of providing kinetic pathways to novel nanocrystal morphologies, compositions, and crystal structures. In the first low temperature method, a new type of chalcogen source (i.e., dialkyl dichalcogenides) is being explored for the synthesis of well-defined semiconductor nanocrystals. The key to this method is the thermal instability of dialkyl dichalcogenides, particularly in the presence of Lewis acids and primary amines. This synthetic methodology is being applied to a wide variety of semiconductor nanocrystals using dialkyl peroxides and dialkyl disulfide, diselenide, and ditelluride reagents, and the resulting optoelectronic and electrochemical properties of the nanocrystals are being measured as a function of size and composition. The second synthetic methodology is based on the kinetically controlled vapor phase delivery of water into a bimetallic alkoxide solution to promote the hydrolysis, nucleation and growth of small perovskite nanocrystals at low temperatures. The key to this method is the slow hydrolysis of a bimetallic alkoxide precursor, which circumvents the requirement for high temperature solid-solid diffusion for crystallization. By taking advantage of this synthesis method, a series of perovskite nanocrystals are being synthesized at very low temperatures and the dielectric properties of the nanocrystals are being studied as a function of their size and composition.NON-TECHNICAL SUMMARY:Despite over fifty years of developments in the field of solid-state chemistry, there are still only a limited number of ways to synthesize materials ? the majority of which require high temperature conditions. As such, there is a need to develop rational methodologies for the synthesis of functional materials under low temperature conditions, much in the same way that organic chemists have developed a very extensive and diverse toolbox of bench-top reactions. Because of the functional size and shape dependent properties of nanoscale (10-9 meters) materials, the impetus to design low temperature synthesis methods also applies to the synthesis of nanocrystals. The goal of this research program is to design new routes to functional nanocrystals using these energy-efficient design principles, which will be significant in the ultimate development of solar energy conversion and energy storage technologies based on these nanocrystal platforms. Integrated into this research plan is the educational objective of bringing the core concepts of solid-state chemistry to students at the university, community college, and high school levels. At the university level, integration of solid-state chemistry into the curriculum will be accomplished via a solid-state chemistry component in a course on Inorganic Structure and Bonding, which is taken by graduate students and advanced undergraduates. At the community college and high school levels, students from underrepresented and economically disadvantaged groups in Los Angeles County will be targeted for participation in a summer internship. Using solar energy conversion and energy storage as compelling working examples, a summer internship will be developed that exposes students to cutting edge and interdisciplinary research occurring at the university setting. This program will consist of a combination of discussions and hands-on work, will illustrate how the scientific method is applied to laboratory research in the context of solid-state chemistry and nanotechnology, and will expose the students to opportunities available to them in science and engineering at the university level and beyond.