From Molecular Scale to Mesoscale: Establishing Structural Control Organic Photovoltaics Using Organic Nanoparticles

Organic photovoltaic devices use an active layer of organic materials that absorbs light and creates free charges to generate electricity. Such organic photovoltaics have many desirable properties as the final devices can be very lightweight, thin, flexible, have low manufacturing costs, and be semitransparent. These properties make them particularly advantageous for myriad of applications: e.g., use on non-planar surfaces, as tinted coatings on windows, any use for charging low power devices. One of the biggest problems preventing organic photovoltaics from being commercialized is controlling the packing of the organic materials within the active layer from the molecular scale through the mesoscale. The state-of-the-art method for preparing active layer offers essentially no control over packing through multiple length scales. In this dissertation, I present a method for controlling the active layer morphology from the molecular scale through the mesoscale using the assembly of organic nanoparticles. The miniemulsion method was used to prepare nanosized particles of each of two active layer components, an electron donor and an electron acceptor. During the nanoparticle synthesis, the internal molecular packing within the particles can be tuned by changing the “oil” (organic soluble) miniemulsion phase. The nanosized domains of each component were directly controlled by tuning the nanoparticle size during synthesis. This provides a large amount of control of the molecular scale packing and the nanoscale packing. Spray-coated assemblies of these nanoparticles, upon removing excess surfactant, were shown to transport charges with mobilities similar to those in films of pristine polymer made by standard drop-cast methods. Donor nanoparticles were mixed with acceptor nanoparticles and shown to form a random binary assembly of nanoparticles with charge conduction pathways. Organic photovoltaic devices were successfully prepared with a mixture of donor nanoparticles and acceptor nanoparticles, and gave performance comparable to analogous devices made by conventional film coating, bulk heterojunction methods. The internal morphology of the active layer films was shown to be easily tuned by changing the nanoparticle diameter or number ratio of donor nanoparticles to acceptor nanoparticles. This method offers the ability to tune the molecular scale, nanoscale, or mesoscale, systematically, packing scales individually or collectively. Therefore, this method can be used to determine systematically what is the optimum active layer morphology for theoretically any donor plus acceptor combination of materials. Also, this method offers a way to control morphology and probe the properties of binary blends of organic materials, in a more general sense, e.g., for making other electronic devices or for charge mobility studies of solid films

Devitrite-based optical diffusers.

Devitrite is a novel material produced by heat treatment of commercial soda-lime-silica glass. It consists of fans of needle-like crystals which can extend up to several millimeters and have interspacings of up to a few hundred nanometers. To date, only the material properties of devitrite have been reported, and there has been a distinct lack of research on using it for optical applications. In this study, we demonstrate that randomly oriented fans of devitrite crystals can act as highly efficient diffusers for visible light. Devitrite crystals produce phase modulation of light because of their relatively high anisotropy. The nanoscale spacings between these needles enable light to be diffused to large scattering angles. Experimentally measured results suggest that light diffusion patterns with beam widths of up to 120° are produced. Since devitrite is an inexpensive material to produce, it has the potential to be used in a variety of commercial applications.HB would like to thank The Leverhulme Trust and Cambridge Philosophical Society for research funding.This is the author accepted manuscript. The final version can be found on the publisher's website at: http://pubs.acs.org/doi/abs/10.1021/nn500155e Copyright © 2014 American Chemical Societ

Graphene-based ultrathin flat lenses

Flat lenses when compared to curved surface lenses have the advantages of being aberration free, and they offer a compact design necessary for a myriad of electro-optical applications. In this paper we present flat and ultrathin lenses based on graphene, the worlds thinnest known material. Monolayers and multilayers of graphene were fabricated into Fresnel zones to produce Fresnel zone plates, which utilize the reflection and transmission properties of graphene for their operation. The working of the lenses and their performance in the visible and terahertz regimes were analyzed computationally. Experimental measurements were also performed to characterize the lens in the visible regime, and a good agreement was obtained with the simulations. This work demonstrates the principle of atom-thick graphene-based lenses, with perspectives for ultracompact integration.</p

Spinning up the Surface: Evidence for Planetary Engulfment or Unexpected Angular Momentum Transport?

In this paper, we report the potential detection of a nonmonotonic radial rotation profile in a low-mass lower-luminosity giant star. For most low- and intermediate-mass stars, the rotation on the main sequence seems to be close to rigid. As these stars evolve into giants, the core contracts and the envelope expands, which should suggest a radial rotation profile with a fast core and a slower envelope and surface. KIC 9267654, however, seems to show a surface rotation rate that is faster than its bulk envelope rotation rate, in conflict with this simple angular momentum conservation argument. We improve the spectroscopic surface constraint, show that the pulsation frequencies are consistent with the previously published core and envelope rotation rates, and demonstrate that the star does not show strong chemical peculiarities. We discuss the evidence against any tidally interacting stellar companion. Finally, we discuss the possible origin of this unusual rotation profile, including the potential ingestion of a giant planet or unusual angular momentum transport by tidal inertial waves triggered by a close substellar companion, and encourage further observational and theoretical efforts.Comment: 18 pages, 9 figures, submitted to AAS Journal

Tunable scattering from liquid crystal devices using carbon nanotubes network electrodes

Liquid crystals are of technological interest as they allow for optical effects which can be electrically controlled. In this paper we present an electro-optical device consisting of nematic liquid crystals addressed by an electrode structure consisting of thin films of polymer wrapped single walled carbon nanotubes (nanohybrids). Thin films of nanohybrids display excellent optical transmission and electrical conduction properties. Due to the randomly organised nanohybrids these composite films produce interesting director profile arrangements within the liquid crystal layers. As a result, enhanced scattering of laser and white light was observed from these liquid crystal cells which bend themselves as electrically controllable optical diffusers and beam shapers

Safely managed hygiene : a risk-based assessment of handwashing water quality

Sustainable Development Goal (SDG) Indicator 6.2.1 requires household handwashing facilities to have soap and water, but there are no guidelines for handwashing water quality. In contrast, drinking water quality guidelines are defined: water must be "free from contamination" to be defined as "safely managed" (SDG Indicator 6.1.1). We modeled the hypothesized mechanism of infection due to contaminated handwashing water to inform risk-based guidelines for microbial quality of handwashing water. We defined two scenarios that should not occur: (1) if handwashing caused fecal contamination, indicated using Escherichia coli, on a person's hands to increase rather than decrease and (2) if hand-to-mouth contacts following handwashing caused an infection risk greater than an acceptable threshold. We found water containing &lt;1000 E. coli colony-forming units (CFU) per 100 mL removes E. coli from hands with&gt;99.9% probability. However, for the annual probability of infection to be &lt;1:1000, handwashing water must contain &lt;2 × 10; -6; focus-forming units of rotavirus, &lt;1 × 10; -4; CFU of Vibrio cholerae, and &lt;9 × 10; -6; Cryptosporidium oocysts per 100 mL. Our model suggests that handwashing with nonpotable water will generally reduce fecal contamination on hands but may be unable to lower the annual probability of infection risks from hand-to-mouth contacts below 1:1000

Evaluating Nuclei Concentration in Amyloid Fibrillation Reactions Using Back-Calculation Approach

Background: In spite of our extensive knowledge of the more than 20 proteins associated with different amyloid diseases, we do not know how amyloid toxicity occurs or how to block its action. Recent contradictory reports suggest that the fibrils and/or the oligomer precursors cause toxicity. An estimate of their temporal concentration may broaden understanding of the amyloid aggregation process. Methodology/Principal Findings: Assuming that conversion of folded protein to fibril is initiated by a nucleation event, we back-calculate the distribution of nuclei concentration. The temporal in vitro concentration of nuclei for the model hormone, recombinant human insulin, is estimated to be in the picomolar range. This is a conservative estimate since the back-calculation method is likely to overestimate the nuclei concentration because it does not take into consideration fibril fragmentation, which would lower the amount of nuclei Conclusions: Because of their propensity to form aggregates (non-ordered) and fibrils (ordered), this very low concentration could explain the difficulty in isolating and blocking oligomers or nuclei toxicity and the long onset time for amyloid diseases