Quantifying organic solar cell morphology: a computational study of three-dimensional maps

Establishing how fabrication conditions quantitatively affect the morphology of organic blends opens the possibility of rationally designing higher efficiency materials; yet such a relationship remains elusive. One of the major challenges stems from incomplete three-dimensional representations of morphology, which is due to the difficulties of performing accurate morphological measurements. Recently, three-dimensional measurements of mixed organic layers using electron tomography with high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) provided maps of morphology with high resolution and detail. Using a simple, yet powerful, computational tool kit, these complex 3D datasets are converted into a set of physically meaningful morphology descriptors. These descriptors provide means for converting these large, complicated datasets (∼5 × 107 voxels) into simple, descriptive parameters, enabling a quantitative comparison among morphologies fabricated under different conditions. A set of P3HT:endohedral fullerene bulk-heterojunctions, fabricated under conditions specifically chosen to yield a wide range of morphologies, are examined. The effects of processing conditions and electrode presence on interfacial area, domain size distribution, connectivity, and tortuosity of charge transport paths are herein determined directly from real-space data for the first time. Through this characterization, quantitative insights into the role of processing in morphology are provided, as well as a more complete picture of the consequences of a three-phase morphology. The analysis demonstrates a methodology which can enable a deeper understanding into morphology control

Material Profile Influences in Bulk-Heterojunctions

The morphology in mixed bulk-heterojunction films are compared using three different quantitative measurement techniques. We compare the vertical composition changes using high-angle annular dark-field scanning transmission electron microscopy with electron tomography and neutron and x-ray reflectometry. The three measurement techniques yield qualitatively comparable vertical concentration measurements. The presence of a metal cathode during thermal annealing is observed to alter the fullerene concentration throughout the thickness of the film for all measurements. However, the absolute vertical concentration of fullerene is quantitatively different for the three measurements. The origin of the quantitative measurement differences is discussed

Neighbor Detection Induces Organ-Specific Transcriptomes, Revealing Patterns Underlying Hypocotyl-Specific Growth.

In response to neighbor proximity, plants increase the growth of specific organs (e.g., hypocotyls) to enhance access to sunlight. Shade enhances the activity of Phytochrome Interacting Factors (PIFs) by releasing these bHLH transcription factors from phytochrome B-mediated inhibition. PIFs promote elongation by inducing auxin production in cotyledons. In order to elucidate spatiotemporal aspects of the neighbor proximity response, we separately analyzed gene expression patterns in the major light-sensing organ (cotyledons) and in rapidly elongating hypocotyls of Arabidopsis thaliana PIFs initiate transcriptional reprogramming in both organs within 15 min, comprising regulated expression of several early auxin response genes. This suggests that hypocotyl growth is elicited by both local and distal auxin signals. We show that cotyledon-derived auxin is both necessary and sufficient to initiate hypocotyl growth, but we also provide evidence for the functional importance of the local PIF-induced response. With time, the transcriptional response diverges increasingly between organs. We identify genes whose differential expression may underlie organ-specific elongation. Finally, we uncover a growth promotion gene expression signature shared between different developmentally regulated growth processes and responses to the environment in different organs

High-Speed Photothermal Patterning of Doped Polymer Films.

Organic semiconductors (OSCs) offer a new avenue to the next-generation electronics, but the lack of a scalable and inexpensive nanoscale patterning/deposition technique still limits their use in electronic applications. Recently, a new lithographic etching technique has been introduced that uses molecular dopants to reduce semiconducting polymer solubility in solvents and a direct-write laser to remove dopants locally, enabling rapid OSC etching with diffraction limited resolution. Previous publications postulated that the reaction that enables patterning is a photochemical reaction between photoexcited dopants with neutral solvent molecules. In this work, we analyze the photoinduced dissolution kinetics of F4TCNQ doped P3HT films using time-resolved in situ optical probing. We find two competing mechanisms that control de-doping and dissolution: the first is the photochemical reaction posited in the literature, and the second involves direct heating of the polymer by the laser, inducing increased solubility for both the polymer and dopant. We show that the wavelength-specific photochemical effect is dominant in low photon doses while the photothermal effect is dominant with high excitation rates regardless of laser wavelength. With sufficiently high optical intensity input, the photothermal mechanism can in principle achieve a high writing speed up to 1 m/s. Our findings bring new insights into the mechanisms behind laser direct writing of OSCs based on dopant induced solubility control and enable ultraprecise fabrications of various device configurations in large-scale manufacturing

Aflatoxin Contamination in Food and Body Fluids in Relation to Malnutrition and Cancer Status in Cameroon

Aflatoxins are food contaminants usually associated with hepatitis, immunodepression, impairment of fertility and cancer. The present work was to determine the presence of aflatoxins in eggs, milk, urine, and blood samples that were collected from various sources and periods; and hepatitis B virus antigen in blood samples. Aflatoxin was found in eggs (45.2%), cow raw milk (15.9%), breast milk (4.8%), urine from kwashiorkor and marasmic kwashiorkor children (45.5%), and sera from primary liver cancer patients (63.9%); HbsAg was also detected in 69.4% of the serum samples, but there was no association between both factors. Both AF and hepatitis B virus seem to be risk factors that could increase the incidence and prevalence rates of malnutrition and cancer in Cameroon