Morphology and Mobility Control for Functional Robust Flexible Electronics and Photovoltaics

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ABSTRACTPIs: Elsa Reichmanis and Martha GroverInstitution: Georgia Tech Research CorporationProposal Number: 1264555Title: Morphology and Mobility Control for Functional Robust Flexible Electronics and Photovoltaics The goal of this research program is to understand and predict the morphology of conjugated polymer materials applicable to flexible electronics, photovoltaics and sensors. The results of this research will enable the design and optimization of robust materials chemistries and the required, associated large-area, large-scale device fabrication process recipes. To exploit the unique capabilities of organic electronics in flexible devices and economical roll-to-roll high throughput printing, high charge carrier mobility is a prerequisite. However, mobility is highly dependent on the final morphology of the thin semiconducting film that serves as the device active layer. Organic semiconductors exhibit domains of crystalline-like order interspersed with amorphous regions, and the size and extent of order within each type of domain influences the molecular packing and subsequent electronic behavior. The morphology in all regions evolves as the film is deposited and processed. Intellectual Merit: Semiconductor morphology in polymer based organic electronics is highly sensitive to the chemistry of a given material, including monomer selection, polymer molecular weight and regioregularity, the solvent, and the substrate. The time-varying process history also impacts the resulting morphology, including temperature, evaporation rate, and the choice of processing method. Understanding the impact of chemistry and processing on the active layer morphology is very limited and is dominated by tedious, observational approaches. A coherent understanding of how π-conjugated semiconductor chains interact, associate and align to form the inter-connected nanocrystallite structures that are essential for charge carrier transport is lacking, and there are far too many design variables to effectively explore this vast design space using a purely empirical approach. In this research program, the PIs will do a synergistic experimental and modeling study based on two specific chemical systems and focusing on three distinct processing modes. Poly(3-hexylthiophene) (P3HT) is the most characterized material to date, and will be used to aid in the initial model-building efforts. They will then build upon the results and extend the studies to promising alternative high mobility systems, such as poly(benzothiazole-sexithiophene) (PBT6), recently designed and developed in the Reichmanis lab. The close coupling of experiments and morphology modeling is unique and will enable a mechanistic understanding of the dynamics of morphology evolution, which will further enable the rational design of robust, organic electronics manufacturing methodologies. Broader Impact: Cheap ubiquitous electronics could transform the world, from solar energy to biosensors to food safety monitoring. The PIs participation in the Georgia Tech Center for Organic Photonics and Electronics (COPE) will amplify the impact of this research, through interactions with COPE industrial associates. The PIs will explore opportunities to directly expose graduate students to industrial research in organic electronics through internships as well as regular research discussions. The graduate students will also benefit from participation (as IGERT affiliates) in the curriculum of the NSF IGERT program on Nanostructured Materials for Energy Storage and Conversion, for which Reichmanis is the PI, and Grover is a thrust leader. As part of this program, the PI and co-PI will initiate a new program aimed at educating female graduate students about paths to faculty positions.