DMREF: Metallic-type transport in polymers: Establishing materials design criteria and predicting structure/property interrelations

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Non-technical Description: A materials design framework is proposed that will provide quantitative insights into what determines charge transport properties in organic semiconductors, and will provide verifiable hypotheses towards accelerated materials discovery. The motivation is partly that, although the multibillion dollar organic electronic industry is based on a unique combination of performance and processability of organic semiconductors, solubility/processability, intermolecular interactions, and other factors impacting delocalization of charge carriers, which determines transport properties, are still not fully understood for these materials. Critical properties can depend subtly on chemical structure and processing conditions and, often, changes in properties and processing parameters are intertwined in non-obvious ways. This creates a daunting task to establish comprehensive structure/processing/property interrelations, often reducing materials discovery to heuristic time-consuming, expensive studies. To unravel the complex interaction of structure/processing and transport properties, a multidisciplinary team of materials chemists, materials engineers, ultrafast spectroscopists, and theorists from Georgia Tech (GT), University of Massachusetts Amherst (UMass), and Los Alamos National Laboratory (LANL), has been assembled. This research will provide critical insights that will enable the quantitative design of materials that optimize both mobility and conductivity. It will also make available to a broad community an extensive database that can be mined to advance materials science discovery platforms, and that will be used in education. We will develop theoretical tools with improved parameterization, allowing the modeling of a broader set of materials. The target materials will be employed in a variety of applications including, amongst others, electrodes, thermoelectric materials, and charge-extraction layers. The highly diverse team will reach out to under-served communities, by recruiting female and under-represented scientists and engineers to carry out research in its shared program, but also through extensive interactions with high schools and the public through a variety of engagement programs and public outreach events.Technical Description: The research addresses fundamental questions of how charge-carrier coherence length and transport properties correlate with specific structural features in doped organic materials. Optical spectroscopies (absorption, photoinduced absorption, photoluminescence, photoluminescence excitation, and two-dimensional coherent excitation spectra), along with thermal analysis and X-ray diffraction data, will be used to construct a database on doped polymers, oligomers and small molecules, utilizing a variety of dopants. Key spectral observables will be modeled with existing theoretical tools at LANL, using first-principle calculations with atomistic approaches, nonadiabatic molecular dynamics simulations, and parameterized Holstein lattice models to simulate quantum dynamics of charges, focusing on spatial coherence lengths of charge carriers in materials. Nonlinear spectroscopies will be used to refine the details of the quantum dynamics models, as they provide details of not only population but also temporal and spatial coherence dynamics. In particular, these measurements can isolate the homogeneous excitation linewidth from the total spectral lineshape, thereby providing a very sensitive probe of spatial coherence, limited by the quantum dynamics that lead to carrier localization. The PIs also plan to release the DMREF Polymeric Semiconductor Toolbox and Database as open source and build a user community around the language by ensuring that interested researchers are able to contribute to the DMREF Polymeric Semiconductor Toolbox and Database codebase. This will allow a wider growth of the project. This aspect is of special interest to the software cluster in the Office of Advanced Cyberinfrastructure, which has provided co-funding for this award.