Collaborative Research: Chemical Control of Polymer/PbS Blends for PV Applications

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Proposals in Collaborative:PI Names: Moule (Lead)Proposal No: 1436273Institution: University of California, Davis PI Name: GanapathysubramanianProposal No:1437636 Institution: Iowa State UniversityPI Name: Ginger Proposal No: 1437016 Institution: University of WashingtonThe sun represents the most abundant potential source of pollution-free energy on earth. Solar cells for conversion of light to electricity based on organic polymers integrated into a photovoltaic (PV) device offer a potentially low-cost route for renewable electricity production if the solar energy conversion efficiency can be improved. The key to improving the efficiency of organic polymer based solar cells is to better understand the molecular arrangement of the materials within the polymer film. This project will apply novel electron microscopy tools to understand how materials processing affects the three-dimensional arrangement of materials in polymer/nanoparticle films designed for photovoltaic (PV) applications. Mixtures of low-cost lead sulfide (PbS) nanoparticles with electrically conducting polymers will be studied because these mixtures have shown recent high photovoltaic efficiency, and because these materials have high imaging contrast by electron microscopy. The electron tomography will generate three dimensional concentration maps of materials within the mixture. These maps will be used to correlate processing conditions to material arrangement within the polymer/nanoparticle film. This information will then be correlated to device performance in order to identify strategies for making better solar cells based on organic polymers. The work will be carried out by a collaborative team that will simultaneously advance the science of polymer/nanoparticle film fabrication, three dimensional electron microscope imaging, and computational analysis of the images to reveal nanoscale structure. This collaborative approach has the potential uncover the structural origin of optical and electronic properties that cannot be measured by any other technique. With respect to education and activities for broadening participation, the project will provide a diverse set of outreach and educational opportunities that include interaction with children through the Boys and Girls Scouts and 4H, public education at well attended local festivals, inclusion of research material in classes, and retention of female engineering students. Technical Description This project will develop and use new electron tomography tools to understand how materials processing affects the three-dimensional arrangement of materials in hybrid polymer/nanoparticle films designed for photovoltaic (PV) applications. Mixtures of low-cost lead sulfide (PbS) nanoparticles with electrically conducting polymers will be studied because these mixtures have shown recent high photovoltaic efficiency, and because these materials have high imaging contrast by electron microscopy. The electron microscopy tool is based on high-angle annular dark-field scanning electron tomography (HAADF-ET) combined with the discrete algebraic reconstruction technique (DART) to generate three-dimensional (3D) material concentration maps with resolution of less than three cubic nanometers for the hybrid organic/inorganic photovoltaic materials. Development of morphology descriptors of the 3D data, including features like the number of phases, concentration ratio in each phase, domain size, domain connectivity, tortuosity of pathways, anisotropy and domain surface area will be measured using graph-based analysis. This information will be used to correlate morphology, structural heterogeneity, and physical distribution of recombination sites in mixed organic/inorganic electronic films to optoelectronic properties and photovoltaic performance. With respect to education and activities for broadening participation, the project will provide a diverse set of outreach and educational opportunities that include interaction with children through the Boys and Girls Scouts and 4H, public education at well attended local festivals, inclusion of research material in classes, and retention of female engineering students.