1,720,986 research outputs found
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
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
Eumelanin-Based Organic Bioelectronics: Myth or Reality?
No full textEumelanins, the black insoluble pigments of human skin, eyes and substantia nigra (neuromelanin), stand today as a unique source of inspiration for the design and implementation of soft biocompatible multifunctional materials for bio-optoelectronic devices. Interest in eumelanins stems from bioavailability, biocompatibility and a peculiar set of physicochemical properties, i.e. broadband absorption in the UV-visible range, intrinsic free radical character, water-dependent hybrid ionic-electronic conductor behaviour, supporting optimistic feelings about a possible rise of eumelanin-mimics as innovative bioinspired solutions for organic bioelectronics. However, a number of conceptual and technological gaps still hinder a rapid progress of melanin-based organic electronics and bioelectronics, including in particular the limited contribution of electronic conductivity and current decay with time under biasing. Herein, we provide a concise overview of the structural and optoelectronic properties of melanins with a view to bringing to focus main issues and challenges en route to bioelectronic applications. Copyright © Materials Research Society 2015
Evaluation of the stability of different encapsulated blue OLEDs
No full textOrganic light emitting diodes (OLEDs) are nowadays the most attractive technology for displays and lighting applications. However, their short lifetime remains the most important limit for their broad commercialization. In particular, blue OLEDs generally present the worst stability respect to the other colors. While the extrinsic degradation can be easily controlled by proper encapsulation, understanding the origins of the intrinsic degradation remains a challenge: up to now, the proposed mechanisms have not considered possible phenomena that can occur during OFF-time periods. In this study, intrinsic degradation phenomena have been studied through shelf life experiments performed at different storage conditions on two types of blue OLEDs. Experiments revealed that physical aging occurs for both types of devices, leading to irreversible time-dependent luminance loss
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
Electron beam curing technology for very high-throughput manufacturing of flexible alternating current powder electroluminescent devices
No full textThick-film alternating current powder-based electroluminescent (ACPEL) succeeds on the market as mature technology for large-area light sources. An additional boost for its development may come from the radiation curing technology. Since it is totally compatible with high-speed roll-to-roll processing, radiation curing can offer multiple advantages to further lower costs and make easier the fabrication process of ACPEL devices. In this paper, the application of the electron beam (EB) curing technology to produce flexible ACPEL devices was explored for the first time. In particular, devices with emitting layer made by EB irradiation were successfully fabricated on poly(ethylene terephthalate) (PET) substrate. Device properties were evaluated and compared with those obtained using the conventional ultraviolet curing process. Smaller driving voltages and higher luminous output were observed for the EB treated samples as a consequence of a more cross-linked polymeric binder of the emitting layer generated. In addition, possible effects of EB overdose were also investigated; experiments revealed that excessively high doses can induce the degradation of both polymeric binder and emitting particles. Therefore, the feasibility of using the EB curing was proven to fabricate ACPEL devices, launching it as the next future technology for more sustainable, very fast, and one-step manufacturing of powder-based alternating current EL devices. © 2016 IEEE
PC70BM n-type Thin Film Transistors: Influence of HMDS Deposition Temperature on the Devices Properties
No full textThis study investigates the influence of the deposition temperature of hexamethyldisilazane (HMDS) on the performances of organic thin film transistors (OTFTs) using the [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as semiconductor. N-type OTFTs have been fabricated using this fullerene derivative, deposited from solution by drop casting technique on HMDS self-assembled monolayer (SAM) deposited at three different temperatures, 7 °C, 25 °C and 60 °C, in order to evaluate the influence of these deposition conditions on the morphology of PC70BM films and on the electrical responses of fullerene derivative-based OTFTs.The effect of the treatments of the surfaces was observed through contact angle measurements. AFM imaging of the deposited material has been used to analyse its structure and morphology. The transistors performances have been evaluated through I vs. V static characterization and parameters extraction.Contact angle vs. HMDS deposition temperature shows the minimum value at 60 °C, instead here field effect mobility presents a maximum. It has been observed that the lower hydrophobicity of the surface of the SAM induces the formation of more homogeneous surface of the PC70BM film, resulting in an increase of the OTFTs performances. © 2016 Elsevier Ltd
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Eumelanin precursor 2-carboxy-5,6-dihydroxyindole (DHICA) as doping factor in ternary (PEDOT:PSS/Eumelanin) thin films for conductivity enhancement
Full text linkThe integration of the pristine not-doped commercial poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) PH1000 with eumelanin, the brown to black kind of melanin pigment, was achieved by dissolving the melanogenic precursors 2-carboxy-5,6-dihydroxyindole (DHICA) in the PH1000 suspension. Solid state oxidative polymerization of the catecholic indole allowed obtaining the ternary blend PEDOT:PSS/eumelanin. The introduction of DHICA into PH1000 produced a noticeable increase in the conductivity of PEDOT thin films akin to that produced by dimethyl sulfoxide (DMSO) treatment, opening up novel strategies for the simultaneous integration of eumelanin polymer and conductivity enhancement of PEDOT containing coatings, as well as the long term goal of replacing PSS by DHICA eumelanin for PEDOT pairing
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