CAREER: Understanding Morphology-Property Correlations in Conjugated Polymer Blends with Nanoscale Optoelectronic Probes

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The scientific goal of this CAREER project is to understand how local phase-separated morphology impacts charge transport, separation, recombination and injection in conjugated polymer blends. The approach involves novel combinations of electrical scanning-probe microscopy with optical excitation and single-molecule optical spectroscopy. Kinetic and thermodynamic phenomena governing phase separation in solution-processed conjugated polymer thin films will be addressed. Immediate attention will be given to processing, characterization, and device performance in blends of semiconducting polymers. Several themes will be initiated including: 1)deconvoluting charge generation and charge transport in nanostructured, photoconductive donor/acceptor blends by making spatially, spectrally, and time resolved charge generation and collection maps with scanning probes; 2)understanding local variations in charge recombination, emission, photochemistry, and exciton-carrier coupling by studying the electroluminescence from both single dopant molecules and nanoscale domains in polymer blends; 3)making high resolution lateral and vertical maps of charge injection and electric field distribution in multi-phase systems as a function of phase composition and polymer conformation at interfaces; 4)mapping the kinetic and thermodynamic governing phase separation in conjugated polymer blends in order to optimize processing into desired morphologies using nanopatterned surface chemistry. Microscopic models will be developed relevant to observed electronic properties as a function of local film structure to assist prediction of which morphologies will meet desired materials performance goals. Predictions will be tested against actual device measurements on films processed to yield the chosen morphology. These studies will be enhanced by close collaboration with both synthetic polymer chemists, and with theorists specializing in electronic structure in complex con-densed-phase systems. %%% The project addresses fundamental research issues in electronic/photonic materials science having technological relevance. The project is interdisciplinary involving the intersection of chemistry, physics, and materials science, and has direct technological applications in photovoltaics and electroluminescent displays--areas readily appreciated by students and the general public. The project will be leveraged to advance major educational goals: to improve undergraduate education through the development and incorporation of computer-based, context-rich problems into the physical chemistry curriculum at the University of Washington; and, to improve graduate education through the establishment of a formal graduate program that will teach verbal commu-nication skills while simultaneously serving outreach efforts targeting underrepresented K-12 groups. The integrated research and teaching activities will lay the foundation for a long-term integrated scientific and educational program that will last beyond the award period.***