Low-Temperature Solution-Processed Electron Transport Layers for Inverted Polymer Solar Cells

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimProcessing temperature is highlighted as a convenient means of controlling the optical and charge transport properties of solution processed electron transport layers (ETLs) in inverted polymer solar cells. Using the well-studied active layer – poly(3-hexylthiophene-2,5-diyl):indene-C60 bisadduct – the influence of ETL processing temperatures from 25 to 450 °C is shown, reporting the role of crystallinity, structure, charge transport, and Fermi level (EF) on numerous device performance characteristics. It has been determined that an exceptionally low temperature processed ETL (110 °C) increases device power conversion efficiency by a factor greater than 50% compared with a high temperature (450 °C) processed ETL. Modulations in device series and shunt resistance, induced by changes in the ETL transport properties, are observed in parallel to significant changes in device open circuit voltage attributed to changes on the EF of the ETLs. This work highlights the importance of interlayer control in multilayer photovoltaic devices and presents a convenient material compatible with future flexible and roll-to-roll processes

ZnO nanorod arrays as electron injection layers for efficient organic light emitting diodes

Nanostructured oxide arrays have received significant attention as charge injection and collection electrodes in numerous optoelectronic devices. Zinc oxide (ZnO) nanorods have received particular interest owing to the ease of fabrication using scalable, solution processes with a high degree of control of rod dimension and density. Here, vertical ZnO nanorods as electron injection layers in organic light emitting diodes are implemented for display and lighting purposes. Implementing nanorods into devices with an emissive polymer, poly(9,9-dioctyluorene-alt-benzothiadiazole) (F8BT) and poly(9,9-di-n-octylfluorene-alt-N-(4-butylphenyl)dipheny-lamine) (TFB) as an electron blocking layer, brightness and efficiencies up to 8602 cd m−2 and 1.66 cd A−1 are achieved. Simple solution processing methodologies combined with postdeposition thermal processing are highlighted to achieve complete wetting of the nanorod arrays with the emissive polymer. The introduction of TFB to minimize charge leakage and nonradiative exciton decay results in dramatic increases to device yields and provides an insight into the operating mechanism of these devices. It is demonstrated that the detected emission originates from within the polymer layers with no evidence of ZnO band edge or defect emission. The work represents a significant development for the ongoing implementation of ZnO nanorod arrays into efficient light emitting devices

Fluorene copolymer bilayers for emission colour tuning in inverted hybrid light emitting diodes

© The Royal Society of Chemistry 2015.We present a robust, entirely solution-based processing route for the deposition of planar F8BT/TFB poly(9,9-dioctylfluorene-alt-benzothiadiazole)/poly(9,9-dioctylfluorene-alt-N-(4-butylphenyl)-diphenylamine) emissive/hole transport bilayers for emission colour tuning in inverted organic-inorganic hybrid light emitting diodes (HyLEDs). Our method allows the facile exploration of TFB thickness for the first time within inverted devices; here we describe the influence of TFB thickness on the device performance. In particular, we demonstrate significant variations in device electroluminescence with highly controlled tunability between green and orange (550 to 610 nm) emission; correlating directly with the thickness of the TFB layer. These changes are in parallel with a 20-fold increase in current efficiency with respect to F8BT-only devices, with our bilayer devices exhibiting luminance values exceeding 11 000 cd m-2. Additionally, through reflectance and angle-dependent electroluminescence measurements we explore the presence of microcavity effects and their impact on device behaviour. We introduce TFB not only as a charge blocking/transporting layer but also as an optical emission-tuning layer

On the geometry of wave solutions of a delayed reaction-diffusion equation

The aim of this paper is to study the existence and the geometry of positive bounded wave solutions to a non-local delayed reaction-diffusion equation of the monostable type.Comment: 25 pages, several important modifications are made. Some references added to the previous versio

Monotone traveling wavefronts of the KPP-Fisher delayed equation

In the early 2000's, Gourley (2000), Wu et al. (2001), Ashwin et al. (2002) initiated the study of the positive wavefronts in the delayed Kolmogorov-Petrovskii-Piskunov-Fisher equation. Since then, this model has become one of the most popular objects in the studies of traveling waves for the monostable delayed reaction-diffusion equations. In this paper, we give a complete solution to the problem of existence and uniqueness of monotone waves in the KPP-Fisher equation. We show that each monotone traveling wave can be found via an iteration procedure. The proposed approach is based on the use of special monotone integral operators (which are different from the usual Wu-Zou operator) and appropriate upper and lower solutions associated to them. The analysis of the asymptotic expansions of the eventual traveling fronts at infinity is another key ingredient of our approach.Comment: 25 pages, 2 figures, submitte

Bioactive Properties and Phenolic Composition of Wood-Aged Beers: Influence of Oak Origin and the Use of Pale and Dark Malts

Ageing beer in contact with wood is a common technological procedure that has been used for centuries to improve colour, structure, and certain flavours. Herein, the impact of the addition of French and American oak wood to two beer styles, pale and dark, on beer phenolic composition (total phenolics, total flavonoids, and HPLC-DAD) and bioactivity (FRAP, DPPH, anti-inflammatory activity in RAW 264.7, and antiproliferative in Caco-2 cells) was assessed. Thirteen phenolics were quantified with values according to previous reports. Dark malt resulted in higher values of total phenolics, to which m-hydroxybenzoic, syringic, p-coumaric acids, and xanthohumol contributed considerably; the exception was (+)-catechin and salicylic acid, which were found to be higher in pale beers. American oak significantly increased 3,4-dihydroxyphenylacetic, vanillic, and syringic acids up to roughly 3, 2, and 10 times, respectively, when compared with French wood. FRAP and DPPH values varied between pale and dark beers, with a less pronounced effect after wood addition. All samples presented considerable cellular antioxidant and anti-inflammatory as well as antiproliferative activity, but differences were found only for the antiproliferative activity, which was higher for the dark beers, which reached about 70% inhibition. Overall, the influence of malts was more pronounced than that of wood, in the studied conditions, highlighting the overwhelming impact of malts on the bioactivity of beer

Thin-film composite forward osmosis membranes functionalized with graphene oxide–silver nanocomposites for biofouling control

© 2016 Elsevier B.V. Innovative approaches to prevent bacterial attachment and biofilm growth on membranes are critically needed to avoid decreasing membrane performance due to biofouling. In this study, we propose the fabrication of anti-biofouling thin-film composite membranes functionalized with graphene oxide–silver nanocomposites. In our membrane modification strategy, carboxyl groups on the graphene oxide–silver nanosheets are covalently bonded to carboxyl groups on the surface of thin-film composite membranes via a crosslinking reaction. Further characterization, such as scanning electron microscopy and Raman spectroscopy, revealed the immobilization of graphene oxide–silver nanocomposites on the membrane surface. Graphene oxide–silver modified membranes exhibited an 80% inactivation rate against attached Pseudomonas aeruginosa cells. In addition to a static antimicrobial assay, our study also provided insights on the anti-biofouling property of forward osmosis membranes during dynamic operation in a cross-flow test cell. Functionalization with graphene oxide–silver nanocomposites resulted in a promising anti-biofouling property without sacrificing the membrane intrinsic transport properties. Our results demonstrated that the use of graphene oxide–silver nanocomposites is a feasible and attractive approach for the development of anti-biofouling thin-film composite membranes