Dissociating the Carbon Nanotube Exciton in Organic- and Inorganic- Semiconductor Blends

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Technical: This project addresses the potential of CNT/polymer/inorganic composite materials for efficient photovoltaic operation. The approach includes: synthesis of blends of semiconducting carbon nanotubes with organic and inorganic semiconductors using wet chemical and solution-based blending techniques; characterization of the internal morphology of these blends as a function of processing conditions and materials selection; identification of composite materials that will form a type II (donor/acceptor) heterojunction with semiconducting carbon nanotubes; studies to determine mechanisms responsible for exciton dissociation and charge collection in carbon nanotube/semiconductor blends; quantification of rates for exciton dissociation, charge separation, and charge recombination in the blends; and, quantification of the electron affinity and ionization potential of monodisperse semiconducting carbon nanotubes. It is expected that photogenerated charge carriers in carbon nanotubes can be dissociated and collected by synthesizing donor/acceptor blends of semiconducting carbon nanotubes with more or less electronegative semiconductors. Emphasis is placed on understanding the interrelationship between synthesis, processing, composition, morphology, and properties of such blends. A variety of semiconductors will be investigated to complement the carbon nanotubes in the blends including fullerene-derivatives, semiconducting polymers, and semiconductor oxides. The morphology of the blends will be characterized via scanning probe and electron microscopy as a function of the processing conditions and materials selections. Electronic transport, photoluminescence quenching, spectrally resolved photocurrent, and transient photo-induced absorption measurements will be used to assess the optoelectronic properties of these materials. Non-Technical: The project addresses basic research issues in a topical area of materials science having high technological relevance. The research will contribute basic materials science knowledge at a fundamental level to new understanding and capabilities for materials combinations with potential for improvements in conversion of solar power to electricity. The scientific investigations will also train students; in addition to supporting one graduate student, the project will promote teaching, training, and learning through the integration of undergraduate students into a research setting. The project also provides support for two summer students in the PI?s laboratory through UW-Madison's SURE/REU (Summer Undergraduate Research Experience and Research Experience for Undergraduates) program. The SURE/REU program primarily supports students in under-represented groups. Additionally, the project supports a UW-Madison undergraduate student for the academic year. Topics such as ethics, how to do research efficiently, problem solving, networking, research safety, experimental procedure, and results presentation will be integrated with day-to-day laboratory training.