NSF/DMR-BSF: Artificial Semiconductor Nanocrystal Molecules for Charge Carrier Separation

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NONTECHNICAL SUMMARYThis award supports theoretical and computational research with an aim to develop a fundamental understanding of the electronic and optical properties in a newly developed family of semiconductor nanocrystals using novel computational methods. Semiconductor nanocrystals are nano-sized (of the order of one billionth of a meter) particles, each containing hundreds to thousands of atoms arranged in a regular framework as in a solid semiconductor such as silicon. These nanocrystals are often referred to as artificial atoms. Remarkably, their chemical and physical properties, such as the color they emit, are flexibly tunable merely by changing their size, unlike real atoms. This has led to their widespread use as building blocks in diverse devices, e.g. to enrich color and enhance energy saving characteristics of the most advanced display screens. In this project, the research team will greatly extend the functionality of semiconductor nanocrystals by taking advantage of their artificial atom character. Carefully tailored semiconductor nanocrystals, serving as artificial atoms, will be combined with others to create a new family of artificial molecules. The particular focus of the project is the investigation of how positive and negative charges, which are created upon light absorption, separate from each other in such artificial molecules. Spatially separating the positive and negative charges in a semiconductor is central for harvesting solar energy (e.g. in solar cells) and transforming it into other, useful forms of energy in a clean and sustainable manner. Working in collaboration with an experimental group, the PI and his research team will focus their theoretical and computational research on understanding the mechanisms of charge separation as a function of the artificial molecules' atomic structure, composition and physical dimensions, and help design new artificial molecules made of semiconductor nanocrystals with desirable functionalities.This project will generate computational tools and fundamental understanding whose utility extends beyond the specific materials investigated. The research will serve as a basis for understanding the basic mechanisms of charge transfer in nanostructures and for designing new photocatalytic and photovoltaic devices that involve light induced charge separation. The project will involve the training of undergraduate and graduate students at the interdisciplinary interface of materials chemistry and engineering. The PI will also organize a summer school at the Telluride Science Research Center focused on modern electronic structure techniques. The lectures given by national and international experts in this school will be converted into online open-access videos for further dissemination of the educational material.TECHNICAL SUMMARYThis award supports theoretical and computational research with an aim to develop a fundamental understanding of the electronic and optical properties in a newly developed family of colloidal quantum dot heterodimers using state-of-the-art stochastic electronic structure techniques. The research team will focus on questions regarding (i) the mechanism of charge transfer at the nanometer scale, (ii) how to control the charge separation efficiencies by changing the dimensions and composition of materials, and (iii) how to model such complex quantum-dynamical models at the minimal model that accounts for all necessary physical processes. Validation of the computational approach will be based on quasiparticle excitations as well as neutral single- and multi-particle excitations. The validated models will then be used to explore the interplay of length scales and timescales on charge transfer mechanisms. The project will also focus on the role of changing the size of the donor/acceptor colloidal quantum dots and the neck connecting them and explore the interplay of Auger- vs. Marcus-like charge transfer mechanisms.This project will generate computational tools and fundamental understanding whose utility extends beyond the specific materials investigated. The research will serve as a basis for understanding the basic mechanisms of charge transfer in nanostructures and for designing new photocatalytic and photovoltaic devices that involve light induced charge separation. The project will involve the training of undergraduate and graduate students at the interdisciplinary interface of materials chemistry and engineering. The PI will also organize a summer school at the Telluride Science Research Center focused on stochastic electronic structure techniques. The lectures given by national and international experts in this school will be converted into online open-access videos for further dissemination of the educational material.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.