Bio: Ross Larsen received his Ph.D. in Physics from Brown University in 1998, where he worked on combining analytical methods of statistical mechanics with numerical simulations to understand the molecular origins of relaxation processes in solution. He performed postdoctoral research at UCSB and UCLA, and later was a Staff Scientist and Lecturer in the Department of Chemistry and Biochemistry at UCLA. Since 2009, he has been a Senior Scientist in the Computational Science Center at the National Renewable Energy Laboratory (NREL). Dr. Larsen initially joined NREL to work on using electronic structure calculations to predict new materials for organic photovoltaics (OPV). He later led NREL’s OPV group and extended the modeling research to include large-scale molecular dynamics simulations of polymer materials, with application to OPV and to radical-containing polymer materials for organic batteries. Other areas of research Ross has been involved in at NREL include: singlet fission in organic crystals, degradation mechanisms in polymeric reflectors, thermal transport mechanisms and phase transitions in nanoparticle aggregates, calculations of surface electronic structure to understand catalytic activity, and nanoparticle-plasmon coupling for solar thermochemical fuel production. He also recently started a project to apply machine learning methods to create chemically aware force fields for molecular dynamics simulations, with initial application to understanding fluctuations of charges (and related electrostatic properties) induced by atomic motions in inorganic halide perovskite materials.
ABSTRACT: Using conjugated organic materials for photovoltaics has many potential advantages over traditional inorganic semiconducting materials. Organic semiconductors are mechanically flexible, endlessly tunable through modification of the molecular constituents, and compatible with inexpensive and scalable processing methods. One application of organic electronic materials is organic photovoltaics (OPV), so-called plastic solar cells. OPV power conversion efficiency recently has risen to over 17% in lab-scale solar cells, and applications ranging from solar windows to roll-out solar panels are currently on the market or in development. In this talk I give an overview of the chemistry and physics underlying OPV performance and I describe an approach to modeling semiconducting polymer materials based on combining quantum mechanical calculations with large-scale classical molecular dynamics simulations. I present results derived using this approach to predict how charges move in six molecularly similar polymer OPV materials. The simulation results demonstrate that seemingly minor alterations in molecular structure can result in large changes in the bulk material, and that the interplay between the material structure and the underlying molecular properties can lead to surprising and counter-intuitive effects on