Development of Reproducible Workflows for Quantum Chemical Parameterization and Validation of Model Organic Photovoltaics

Solar cells made from organic photovoltaic (OPV) materials have the potential to provide sustainable solar power generation due to their low manufacturing cost and processability. Molecular dynamics (MD) simulations allow for close examination of the behavior and properties of OPVs. The first step of simulating a new compound in MD is deciding how to apply force field parameters based on the chemical structure of the molecule, and if the chemical environment is not defined in the forcefield, then new parameters must be created. Here we develop and compare two computational tools for identifying bond, angle, and dihedral constraints that are missing from a forcefield, and perform quantum chemical calculations to parameterize these missing components. We set up the Espaloma and QUBEKit software stack on the Borah high performance computing (HPC) cluster, utilize SMILES strings to specify minimal molecular snippets, and parameterize models of Y6 and BTO, which have recently demonstrated power conversion efficiency over 17%. We perform MD simulations of BTO and Y6 across a range of densities and temperatures, and analyze structure using both real and frequency space techniques. We observe no evidence of crystal structures or other long-range periodicities, which suggests that these disordered morphologies have high charge transport despite their lack of order, in contrast to other OPV materials

Evaluation of a pediatric blood filter for whole blood transfusions in domestic chickens (Gallus gallus)

Blood filters that prevent clots, microaggregates, and other debris from being passed from the donor blood into the recipient are an essential component of blood transfusions in mammalian species but have not been consistently recommended in avian transfusions. To evaluate the hemolytic effect of an 18-microm filter in chickens, 9 mL of blood was collected from each of 30 chickens (Gallus gallus) into a syringe containing 1 mL of citrate phosphate dextrose adenine (CPDA-1) to obtain a 1:9 dilution of CPDA-1 to blood. One half of each sample was then run through a pediatric blood filter before separating the plasma. The level of hemolysis in both filtered and unfiltered portions was determined by measuring the concentration of free hemoglobin in the plasma. All samples had low hemoglobin concentrations (less than 30 mg/dL) with no significant difference between the unfiltered and filtered portions. Based on these results, an 18-microm blood filter can be used safely for blood transfusions in domestic chickens as it does not cause significant hemolysis

Computational Challenges to Predicting Morphology of Large Macromolecule Blends

Organic molecules have emerged as a modern alternative to silicon as photovoltaic materials for solar cell applications. This is credited to their low manufacturing costs and ease of processability. Y6 and BTO have gained recognition as promising acceptor molecules for these devices, having demonstrated a power conversion efficiency of over 17%. Due to their relative recency, however, little is known about the morphology and charge transfer properties of these materials. Our work involves studying a mixture of these molecules under a computational lens: Molecular Dynamics (MD) provides us with information about the morphology and Kinetic Monte Carlo (KMC) simulations inform us about the charge carrier transport performance. Understanding the relationship between molecular structure and device efficiency will help support the engineering of efficient, affordable solar cells

Patching Force Fields of Organic Materials Through Open Scientific Software Development

Solar cells made from organic photovoltaic (OPV) materials have the potential to provide sustainable solar power generation due to their low manufacturing cost and processability. Molecular dynamics (MD) simulations allow for the pre-screening of OPVs more efficiently than wet lab experimentation alone. Doing so requires the description of interaction potentials between simulation elements within the system. Therefore, the first step of simulating a new compound with MD is deciding how to apply forcefield parameters based on the chemical structure of the molecule, and if the chemical environment is not defined in the forcefield, then new parameters must be created. Here we develop and use computational tools for identifying bond, angle, and dihedral constraints that are missing from a forcefield, and perform quantum chemical calculations to parameterize these missing components. We set up the QUBEKit software stack on the Borah high performance computing (HPC) cluster, utilize SMILES strings to specify minimal molecular snippets, and parameterize models of Y6 and BTO, which have recently demonstrated power conversion efficiency over 17%

Understanding Packing of New Compounds for Inexpensive Solar Panels

We perform molecular dynamics simulations to investigate the structure of two kinds of molecules that could be used in high-efficiency organic solar cells. We consider a branched molecule (ITIC) and polymer (PTB7) and measure their spatial correlations and dynamics as a function of temperature and density. Using radial distribution functions to measure local correlations we identify a density threshold above which both types of molecules become too entangled to rearrange. We find increased spatial correlations at lower temperatures when densities are below the entanglement threshold and fundamentally different molecular packings of the branched ITIC molecules versus the more linear PTB7 molecules that can more easily align. Our findings provide insight into the molecular packings that could correlate with better charge transport in organic solar cells and inform strategies for more efficient and informative future simulations

Using Computational Tools to Accelerate Discovery of High-Efficiency Solar Cell Materials

High-efficiency organic photovoltaic (OPV) materials made with non-fullerene electron acceptors are exciting because of their potential for realizing solar power that pays for its capital cost in weeks rather than decades. Optimizing these materials is challenging because of the number of (a) possible non-fullerene acceptors, (b) polymers to mix them with, and (c) ways these two compounds can be processed together to make an OPV device. Here we develop computational tools for screening candidate OPV blends that robustly assemble morphologies that convert sunlight into electricity using reproducible high-performance computing (HPC) workflows that enable programmatic specification of OPV structure prediction. We develop open source tools: the Molecular Simulation Design Framework (MoSDeF) for general molecular simulation infrastructure, PlanckTon for launching molecular dynamics simulations of blends, and MorphCT for predicting charge mobilities of the equilibrated morphologies. Specific incorporation of SMARTS and SMILES chemical grammars, new binary file formats, and modular open source quantum chemical calculation engines have contributed to our simplified, more reproducible workflows. This has also helped with containerization of both MorphCT and PlanckTon, which makes them easier to deploy on HPC resources. We briefly describe collections of hundreds of simulation jobs and the understanding of OPV physics enabled by these software developments

Validating Structural and Thermodynamic Properties of Nonfullerene Acceptors for Organic Photovoltaics

A single junction solar cell can possess a theoretical maximum efficiency of 33.7%; the closer solar cells are to this value, the harder it is to improve efficiency. Organic photovoltaics (OPVs)—solar materials made from organic compounds—have recently gained interest in scientific and industrial communities because of their increasing performance in power conversion efficiency. In addition, OPVs can be manufactured inexpensively, thus possessing an energy payback time that outperforms other solar cells. Their potential low cost comes from a combination of inexpensive manufacturing techniques like roll-to-roll and screen printing, low-cost raw materials, and the materials’ ability to self assemble under ambient conditions. Our lab generates Molecular Dynamic (MD) simulations and uses analysis techniques such as radial distribution functions (RDF), mean square displacement (MSD) plots, and diffraction patterns for different organic molecules under varying conditions to identify the most robust morphologies for self-assembly and charge transport. Our results reveal promising active layer candidates possessing the characteristics of effective charge transport and close packing of layers that are desired for future organic solar cells

Multiple tracheal resections and anastomoses in a blue and gold macaw (Ara ararauna)

A 1.5-year-old, male blue and gold macaw (Ara ararauna) was anesthetized for a health examination and blood collection. The following day it was returned for episodes of coughing. The bird was presented again 13 days after the initial presentation with severe dyspnea. A tracheal stenosis was diagnosed by endoscopy and treated by surgical resection of 5 tracheal rings and tracheal anastomosis. The bird was discharged but returned 2 days later with a recurrent stenosis. Bougienage and balloon dilation of the stenotic area were performed separately; each resulted in less than 48 hours\u27 improvement in clinical signs after treatment. A second tracheal resection and anastomosis was performed, during which an additional 10 tracheal rings were removed. This second anastomosis was significantly more difficult to complete given the marked variation in diameter of the proximal and distal tracheal segments. The macaw recovered without complication and has had no recurrence of respiratory abnormalities 2 years after the second surgery. This report describes the longest total tracheal segment to be resected, followed by tracheal anastomosis, in a psittacine bird. The positive outcome in this case suggests that, when surgical therapy is elected, an aggressive approach is necessary to prevent recurrence of tracheal stenosis. In addition, macaws can recover well even after significant lengths of the trachea are resected