Minimizing Sheet Resistance of Organic Photovoltaic Cell Top Contact Electrode Layer: Silver Nanowire Concentration vs. Conductive Polymer Doping Concentration

The top contact electrode layers of nine organic photovoltaic cells were prepared with two varying factors: three Silver nanowire (AgNW) densities deposited on a conductive polymer doped with three concentrations. Silver’s low sheet resistance of 20-Ω/sq is hypothesized to lower the sheet resistance of the anode layer and thus enhance the overall efficiency of the cell. Four-point probe measurements indicated that increasing AgNW density in the top contact electrode layer of an organic photovoltaic cell significantly reduces sheet resistance from 52.2k-Ω/sq to 18.0 Ω/sq. Although an increase in doping concentration of the conductive polymer reduced sheet resistance in low AgNW density samples from 52.2k-Ω/sq to 5.10k-Ω/sq, only a minor decrease from 34.7-Ω/sq to 29.2-Ω/sq was found in the higher AgNW density samples. To explain these patterns, we propose a transition in charge carrier conduction mechanism from one of resistors in series (AgNW and polymer matrix), controlled by the resistance of the conductive polymer, to that of a parallel circuit, with resistance controlled by the resistance of silver. Proposed models are supported by the number of disjoints between AgNWs found in Scanning Electron Microscope characterizations at 20,000X magnification. The number of disjointed AgNWs within 2.8 µm x 3.2-µm sections on the electrode surface decreased from an average of two to zero with increasing AgNW density. Atomic Force Microscopy characterizations portrayed increased RMS roughness due to AgNW agglomeration, ring shaped wire orientation and a random distribution of particles that potentially raise sheet resistance with increased contact resistance

ELECTROPHORETIC DISPLAYS WITH TUNABLE, ANGLE-INDEPENDENT COLOR

Electrophoretic displays (EPDs), which exploit the surface charge of microparticles to control their deposition, have become widely available in consumer electronics, such as e-readers and smartwatches. However, a full-color EPD has yet to be demonstrated and commercialized. Here, we demonstrate colloidal assemblies of engineered quasi-amorphous photonic materials, using pigmentary α-Fe2O3/SiO2 core/shell nanoparticles, exhibiting non- iridescent tunable colors which can be tuned electrophoretically. The observed colors result from combination of colloidal particle arrangements, giving rise to structural color, along with the inherent pigmentary color of the α-Fe2O3/SiO2 nanoparticles. Colloidal particle assemblies of α-Fe2O3/SiO2 core/shell nanoparticles, and therefore the resulting colors, can be manipulated by shell thickness, particle concentration and external electrical stimuli. Dynamic tunability of α-Fe2O3/SiO2 nanomaterials in the visible wavelengths is demonstrated using reversible electrophoretic deposition with a noticeable difference between transmitted and reflected colors. The distinct contrast generated can be exploited for tunable display applications. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-704082

In-situ USAXS/SAXS Investigation of Tunable Structural Color in Amorphous Photonic Crystals during Electrophoretic Deposition

Amorphous photonic crystals (APCs) formed via electrophoretic deposition (EPD) exhibit non-iridescent, angle-independent, structural colors believed to arise from changes in the particle-particle interactions and inter-particle spacing, representing a potential new paradigm for display technologies. However, inter-particle dynamics on nanometer length scales that govern (and enable control over) the displayed color, crystallinity, and other characteristics of the photonic structures, are not well understood. Unfortunately, typical lab-based characterization techniques such as SEM, TEM, and Computed Tomography (CT) are generally performed ex-situ once the sample deposit has been dried. In this work, in-situ USAXS/SAXS/WAXS studies of three-dimensional colloidal particle arrays (of varying particle size and concentration) were performed in order to identify their structural response to applied external electric fields. This data was compared to simultaneously acquired UV-Vis spectra to tie the overall electrically induced structure of the APCs directly to the observed changes in visible color. The structural evolution of the APCs provides new information regarding the correlation between nano-scale particle-particle interactions and the corresponding optical response. To our knowledge, there has been no other prior studies examining the structure of APCs during the application of an electric field. This novel, in-situ USAXS study has helped to gain a better fundamental understanding of how the properties of APCs can be controlled for the advancement of optical displays. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-725437-DRAF

History of Education in Oppressed Groups: A Comparative Study of Deaf and Native American Education

This thesis is a comparative study of the education of two minority cultural groups who have a strong history of oppression in the American culture. This paper explores the similarities and differences in the histories of educating Native American and deaf/hard of hearing children. My original goal when I started this research project was to answer the question ‘why are residential schools for the deaf and hard of hearing still used to educate this minority group while residential schools for Native American children are not as prevalent’. However, after further research, I realized that it was not an issue of the residential schools themselves, but of funding. This thesis is seeking to compare histories, education, and achievement levels of both minority groups in order to address a larger issue: are minority students being taught in such a way that facilitates their learning? I feel that this is an important issue because the number of children in the education system belonging to minority groups in our country is on the rise. We need to be prepared to properly educate them in order to better prepare them for the workforce

Volumetric Additive Manufacturing of Silica Glass with Microscale Computed Axial Lithography

Glass is increasingly desired as a material for manufacturing complex microscopic geometries, from the micro-optics in compact consumer products to microfluidic systems for chemical synthesis and biological analyses. As the size, geometric, surface roughness, and mechanical strength requirements of glass evolve, conventional processing methods are challenged. We introduce microscale computed axial lithography (micro-CAL) of fused silica components, by tomographically illuminating a photopolymer-silica nanocomposite which is then sintered. We fabricated 3D microfluidics with internal diameters of 150 micrometers, freeform micro-optical elements with surface roughness of 6 nm, and complex high-strength trusses and lattice structures with minimum feature sizes of 50 micrometers. As a high-speed, layer-free digital light manufacturing process, micro-CAL can process extremely viscous nanocomposites with high geometric freedom, enabling new device structures and applications

Isolating Chemical Reaction Mechanism as a Variable with Reactive Coarse-Grained Molecular Dynamics: Step-Growth versus Chain-Growth Polymerization

We present a general approach to isolate chemical reaction mechanism as an independently controllable variable across chemically distinct systems. Modern approaches to reduce the computational expense of molecular dynamics simulations often group multiple atoms into a single “coarse-grained” interaction site, which leads to a loss of chemical resolution. In this work we convert this shortcoming into a feature and use identical coarse-grained models to represent molecules that share nonreactive characteristics but react by different mechanisms. As a proof of concept, we use this approach to simulate and investigate distinct, yet similar, trifunctional isocyanurate resin formulations that polymerize by either chain- or step-growth. Because the underlying molecular mechanics of these models are identical, all emergent differences are a function of the reaction mechanism only. We find that the microscopic morphologies resemble related all-atom simulations and that simulated mechanical testing reasonably agrees with experiment

Nickel Complexes of C‑Substituted Cyclams and Their Activity for CO₂ and H⁺ Reduction

Several nickel­(II) complexes of cyclams bearing aryl groups on the carbon backbone were prepared and evaluated for their propensity to catalyze the electrochemical reduction of CO₂ to CO and/or H⁺ to H₂, representing the first catalytic analysis to be performed on an aryl–cyclam metal complex. Cyclic voltammetry (CV) revealed the attenuation of catalytic activity when the aryl group bears the strong electron-withdrawing trifluoromethyl substituent, whereas the phenyl, <i>p</i>-tolyl, and aryl-free derivatives displayed a range of catalytic activities. The gaseous-product distribution for the active complexes was determined by means of controlled-potential electrolysis (CPE) and revealed that the phenyl derivative is the most active as well as the most selective for CO₂ reduction over proton reduction. Stark differences in the activity of the complexes studied are rationalized through comparison of their X-ray structures, absorption spectra, and CPE profiles. Further CV studies on the phenyl derivative were undertaken to provide a kinetic insight

Nickel Complexes of C‑Substituted Cyclams and Their Activity for CO₂ and H⁺ Reduction

Several nickel­(II) complexes of cyclams bearing aryl groups on the carbon backbone were prepared and evaluated for their propensity to catalyze the electrochemical reduction of CO₂ to CO and/or H⁺ to H₂, representing the first catalytic analysis to be performed on an aryl–cyclam metal complex. Cyclic voltammetry (CV) revealed the attenuation of catalytic activity when the aryl group bears the strong electron-withdrawing trifluoromethyl substituent, whereas the phenyl, <i>p</i>-tolyl, and aryl-free derivatives displayed a range of catalytic activities. The gaseous-product distribution for the active complexes was determined by means of controlled-potential electrolysis (CPE) and revealed that the phenyl derivative is the most active as well as the most selective for CO₂ reduction over proton reduction. Stark differences in the activity of the complexes studied are rationalized through comparison of their X-ray structures, absorption spectra, and CPE profiles. Further CV studies on the phenyl derivative were undertaken to provide a kinetic insight