This collaborative project brings together faculty and scientists at the University of Denver and the University of Colorado at Boulder to study new materials and concepts in organic photovoltaics (OPV). It combines new mathematical methods to describe photonic processes with novel plasmonic nanostructures for enhancing optical absorption and new organic semiconductors for control of exciton flow and charge carrier dynamics. The theoretical foundations of linear and nonlinear processes in surface plasmons and their interactions with organic chromophores are explored, and the interplay between surface plasmons and Förster Resonant Energy Transfer (FRET) is investigated. New organic molecules are synthesized that incorporate graphenic and other moieties with exceptional charge transport and excited-state properties along with liquid-crystalline functionality for improved molecular ordering. The overall goal is to enhance the density of excitons created in OPV devices to enable higher efficiencies as well as coherent control of excited state dynamics and multiexciton phenomena. The work entails significant collaborations with the National Renewable Energy Laboratory and the University of Toronto.

This project aims to advance the fundamental knowledge of OPV materials and mechanisms and to provide impetus for moving OPV to the broader market as a low-cost solar energy technology that can be produced on a truly large scale. The interdisciplinary nature of the project gives graduate students and postdoctoral trainees exposure to a variety of research settings and fosters their learning and career growth. The project generates educational materials that are broadly disseminated through websites and through the National Science, Technology, Engineering, and Mathematics Education Digital Library (NSDL). Outreach activities for local high school science teachers in the Denver and Boulder areas enable hands-on experience with intensive workshops on solar energy and nanotechnology. Demonstrations, exhibits, and instructional materials are provided to Colorado institutions such as the Wings Over the Rockies Air & Space Museum and the Mamie Dowd Eisenhower Library.

Project Report

The overall goal of this project was to investigate new photonic phenomena accuring at high excitation densitites in organic molecular systems, with the aim of ultimately enabling higher efficiency photovoltaic devices for efficient solar energy conversion. The project was a collaboration between the University of Denver, the University of Colorado Boulder, the Colorado School of Mines, and the National Renewable Energy Laboratory (NREL). The work led to a greater understanding of novel nonlinear optical upconversion mechanisms, design and construction of optimized nanostructures to enhance light absorptionn, the development of tailored organic molecules and macromolecular structures, and an improved understanding of fundamental linear and nonlinear optical phenomena. Intellectual Merit. Specific intellectual merit outcomes included (i) the development of an electric-field response discotic liquid crystalline material based on a hybrid multichromophore molecule, (ii) demonstration of enhanced light absorption and charge collection in an organic photovoltaic material with the implementation of a fractal electrode geometry, and (iii) demonstration of optical plasmon modes in an organic photovoltaic polymer. The project also resulted in the first demonstration a new optical upconversion phenonemon known as Cooperative Energy Pooling, involving the adding the energies of low energy photons created in mixtures of organic molecular chromophores. Overall the project resulted in both an improved fundamental understanding of several topics in the control of nonlinear optical phenomena as well as the development several practical molecular structures and nanograting devices. Broader Impacts. The outcomes are expected to propel further work on the topic of nonlinear control of light for enhanced photonic properties of organic and hybrid solar energy conversion devices. The phenomena studied can also be applied to optical upconversion for fields such as biomedical imaging based on two photon spectroscopy and in nonlinear optics in general. The project resulted in training of postdocs and graduate students in an interdisciplinary setting that crossed boundaries between multiple fields and involved collaborations between several universities and a nationa laboratory, providing a uniqued educational experience to the participants.

National Science Foundation (NSF)
Division of Chemistry (CHE)
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Suk-Wah Tam-Chang
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University of Denver
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