Designing Intermolecular Interactions for High-Performance Small-Molecule Bulk Heterojunctions

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Technical Description: In this project, optoelectronic properties of small-molecule donor-acceptor materials are systematically explored, with the ultimate goal of developing soluble donor-and-acceptor molecules for efficient small-molecule bulk heterojunction solar cells and novel sensitizers (acceptors) for photorefractive devices with improved properties. The project aims to fulfill the following three objectives: to establish dependence of charge photogeneration, transport, and recombination on the relative energies of the donor-and-acceptor molecules and molecular packing (macroscopic level); to quantify contributions of the donor-and-acceptor domains and donor-acceptor interfacial areas to charge photogeneration, transport, and recombination depending on the donor-and-acceptor molecules and their packing (microscopic level); and to determine molecular photophysics, three-dimensional alignment and domain formation tendencies, of guest acceptor molecules in crystalline donor hosts depending on the molecular structures of the donor-and-acceptor molecules and disorder (single-molecule level). Effects of sample fabrication and processing are also studied. In order to fulfill these objectives, measurements of time-resolved photocurrent (including scanning photocurrent microscopy) and time-resolved fluorescence (including near-field scanning optical microscopy and single-molecule fluorescence spectroscopy) combined with numerical modeling are carried out.Non-technical Description: One of the most important aspects of the project is its potential impact on solar and photorefractive three-dimensional display technology, as well as on other optoelectronic applications based on solution-processable organic films. The project integrates fundamental physics and chemistry with materials design and device technologies and thus provides interdisciplinary educational resources and infrastructure for postdoctoral researchers and graduate and undergraduate students contributing to research. The PI makes active efforts to involve undergraduates, including female and minority students, in the project. Based on research results, the research team develops educational materials, demonstrations, and web tutorials that are introduced into graduate and upper-level undergraduate physics and engineering courses to deepen students' understanding of the material as well as incorporated into events for college freshmen and high-school students.