1,721,084 research outputs found
Synthesis of highly regioregular poly[3-(4-alkoxyphenyl)-thiophene]s by oxidative catalysis using copper complexes
No full textA novel, easy, and cost-effective synthetic procedure is reported for the production of very highly regioregular poly[3-(4-alkoxyphenyl)thiophene]s by means of oxidative coupling. Four copper complexes were synthesized and used as catalysts to obtain polymers with higher regioregularity compared to the previous oxidative coupling methodologies reported in the literature and similar to that obtained by McCullough and Rieke methods in the synthesis of poly-3-alkylthiophenes. The regioregularity of the synthesized polymers was investigated by UV-Visible characterization on polymer thin films and 1H NMR analysis. The remarkable potentialities of these polymers have emerged from field-effect transistor mobility measurements operated on devices with bottom-contact configuration and hexamethyldisilazane-treated SiO 2 gate dielectric, showing a well-defined p-type field-effect response and maximum mobility values in air higher than 10-4 cm 2 V-1 s-1. © 2013 Wiley Periodicals, Inc
Optical properties of ionic liquid passivated CdSe/ZnS quantum dots dispersed in POC copolymer
No full textA new blue emitter oxadiazole/carbazole copolymer has been synthesized and combined with CdSe/ZnS quantum dots (QDs). Surface passivation of the QDs by ionic liquids was crucial to improve their compatibility with the polymer allowing the deposition of homogeneous nanocomposites films. The nanocomposites have been characterized by thermogravimetric analysis, infrared, UV-visible absorption, and photoluminescence spectroscopy. The emission spectra of nanocomposites show a wide spectrum from blue to orange wavelengths due to the combination of colors emitted by the polymer and QDs, respectively. © 2013 Society of Plastics Engineers
Eumelanin–PEDOT:PSS Complementing En Route to Mammalian-Pigment-Based Electrodes: Design and Fabrication of an ITO-Free Organic Light-Emitting Device
No full textThe growing interest toward biocompatible and bioinspired materials is boosting the investigation and the engineering of natural products as active components in electronic devices. The human pigment melanin, and particularly its subgroup composed by the eumelanins, the black-brown pigments derived from the oxidative polymerization of L-3,4-dihydroxyiphenylalanine (l-DOPA) via 5,6-dihydroxy-indole intermediates are increasingly emerging as valuable candidates for organic (bio)electronics applications. Capitalizing on a recently developed protocol to prepare high quality eumelanin coatings, this paper reports herein the design and the integration of standard commercial poly(3,4-ethylenedioxythiophene) with the poly(styrenesulfonate) (PEDOT:PSS) with eumelanin pigment. The new blend has made it possible to obtain a water stable quite transparent thin film, able to operate as an electrode for organic devices, complementing the PEDOT:PSS conductivity with the peculiar eumelanin properties, including adhesion, water stability, and ionic–electronic conductivity. As proof of concept, an unprecedented indium tin oxide-free organic light emitting diode implementing an eumelanin–PEDOT layer as the anode is fabricated and characterized. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
Round robin performance testing of organic photovoltaic devices
No full textThis study addresses the issue of poor intercomparability of measurements of organic photovoltaic (OPV) devices among different laboratories. We present a round robin performance testing of novel OPV devices among 16 laboratories, organized within the framework of European Research Infrastructure Project (SOPHIA) and European Energy Research Alliance (EERA). Three types of OPVs with different structures, dimensions and encapsulations are studied and compared with reference Si solar cells certified by accredited laboratories. The agreement of the measurements of these among different laboratories is analyzed by focusing on testing procedures, testing equipment and sample designs. A number of deviations and pitfalls are revealed and based on the analyses, a set of recommendations are suggested for improving the agreement among the measurements of such OPV technologies. © 2013 Elsevier Ltd
Analysis of HMDS self-assembled monolayer Effect on Trap Density in PC70BM n-type Thin Film Transistors through Admittance Studies
No full textIn this work, n-type organic thin film transistors (OTFTs) were fabricated in the bottom-gate bottom-contact configuration, depositing a fullerene-derived semiconductor (PC70BM) by drop-casting technique on SiO2 substrates treated with a self-assembled monolayer, namely the HMDS. The influence of the deposition temperature of the HMDS on the device performance was investigated, using three different temperatures. The relationship between the properties of the resulting semiconductor films and the electrical characteristics of the transistors was evaluated through admittance measurements. The frequency response of the devices vs. the bias was interpreted applying an electrical equivalent circuit to model the properties of the semiconductor and of the transistor conductive channel. The proposed model shows the critical role played by the quality of the insulator-semiconductor interface on the traps density in the semiconductor, and therefore on the increase of the mobility and on the reduction of the threshold voltage of the transistors. © 2017 Elsevier Ltd
Analysis of the persistent photoresponse of C8BTBT transistors in the near-bandgap spectral region
No full textThe variations in physical parameters of an organic field-effect transistor having dioctylbenzothieno[2,3-b]benzothiophene (C8BTBT) as the channel semiconductor were investigated under different light irradiation conditions at wavelengths of 350 nm, 370 nm, 400 nm and by increasing exposure doses. The progress of the electro-optical history of the transistor was evaluated by repeating I-V scan cycles both in the dark and under light exposure. The information recorded upon different exposure times was used to detect the photoactivated charge-trapping effects. The device showed a stable I-V response in the dark bias (VDS = -10 V, -10 V ≤ VGS ≤ +10 V) conditions and a persistent threshold voltage (VT) shift under illumination at all irradiation wavelengths. We suggested that the observed dose-dependent VT drifts were due to charge retention in trap sites within the organic semiconductor. The threshold voltage was recognized as the main parameter affected by charge retention. VT variations were modelled versus time through a single exponential revealing a maximum in charge relaxation times for irradiations at wavelengths of 370 nm, in proximity of the C8BTBT bandgap energy. Furthermore, bias-stress effects and persistent photoinduced VT drifts were found to depend on comparable characteristic times. Therefore, a common nature for both the bias-stress decay and relaxation from photoexcitation mechanisms is likely. © 2015 Elsevier B.V. All rights reserved
Nanocomposite polymer carbon-black coating for triggering pyro-electrohydrodynamic inkjet printing
No full textThe pyro-electrohydrodynamic (EHD) manipulation of liquids has been discovered and demonstrated recently as a high resolution printing technique avoiding the use of nozzles and external electrodes. The activation of the pyro-electric effect is usually achieved on ferroelectric crystals by an external heating source or by an infrared laser. Here, we show an original modality for triggering the pyro-EHD process through a light-absorbing polymer nanocomposite thin layer deposited on the ferroelectric substrate, thus overcoming some limitations of the previous configuration. Significant simplification and compactness of the set-up is achieved thanks to the nanocomposite coating, since a commercial low-cost white-light halogen lamp can be adopted to trigger the pyro-jetting process from a liquid reservoir. Remarkably, high resolution is achieved in dispensing very high viscous liquids. Practical demonstrations in polymer optical microlenses direct printing using polydimethylsiloxane and poly(methyl methacrylate) are finally reported to validate the approach in handling high-viscous polymers for practical applications. © 2015 AIP Publishing LLC
Photosensing properties of pentacene OFETs based on a novel PMMA copolymer gate dielectric
No full textIn the present work, bottom-gate top-contact organic field effect transistors (OFETs) were fabricated by evaporating a pentacene semiconductor film on top of a new insulating poly(methyl methacrylate) (PMMA) copolymer containing methacrylate units. The PMMA copolymer was synthesized in order to combine the well-known insulating properties of PMMA with the possibility to be efficiently photocured enabling photopatterning-based organic circuitry integration processes. The properties of the pentacene layer deposited on ITO/PMMA copolymer stack were studied through morphological and structural analyses. Device photoresponses and photoexcitated transients were investigated and compared to reference devices based on standard PMMA gate dielectric. © 2015 IEEE
Melanin-inspired organic electronics: Electroluminescence in asymmetric triazatruxenes
No full textAbstract The oxidative polymerization of 5,6-dihydroxyindoles and related hydroxyindoles at pH<3 is diverted from the usual eumelanin-forming pathway to produce mixtures of symmetric and asymmetric triazatruxenes (TATs), which could be separated and characterized for their opto-electronic properties with the aid of TD-DFT calculations. Data showed that the asymmetric isomers exhibit higher fluorescence quantum efficiencies, lower HOMO-LUMO gaps, better film homogeneity, and a more definite aggregation behavior than the symmetric counterparts, suggesting promising applications in organic electronics. The enhanced luminance exhibited by the OLED devices fabricated with blends of the synthesized TATs in poly-9-vinylcarbazole confirmed the potential of the asymmetric skeleton as new versatile platform for light-emitting materials. From black melanins to light-emitting triazatruxenes: Melanin-inspired triazatruxenes have been synthesized and their opto-electronic properties studied (see figure). The comparision of the electroluminescence and luminance of the OLED devices fabricated with triazatruxenes suggests the potential of the asymmetric platform as a new central core for light-emitting materials. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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