1,720,961 research outputs found
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
Overcoming Challenges in OLED Technology for Lighting Solutions
No full textIn academic research, OLEDs have exhibited rapid evolution thanks to the development of innovative materials, new device architectures, and optimized fabrication methods, achieving high performance in recent years. The numerous advantages that increasingly distinguish them from traditional light sources, such as a large and customizable emission area, color tunability, flexibility, and transparency, have positioned them as a promising candidate for various applications in the lighting market, including the residential, automotive, industrial, and agricultural sectors. However, despite these promising attributes, the widespread industrial production of OLEDs encounters significant challenges. Key considerations center around efficiency and lifetime. In the present review, after introducing the theoretical basis of OLEDs and summarizing the main performance developments in the industrial field, three crucial aspects enabling OLEDs to establish a competitive advantage in terms of performance and versatility are critically discussed: the quality and stability of the emitted light, with a specific focus on white light and its tunability; the transparency of both electrodes for the development of fully transparent and integrable devices; and the uniformity of emission over a large area
ITO sputtering study for transparent OLED top electrode
No full textOrganic Light Emitting Diodes (OLEDs) are a cutting-edge lighting technology that allows to create thin, light weight, diffuse-emitting, glare-free, and even transparent light sources having low power consumption, wide color gamut, fast response time, and precise dimming. Transparent OLEDs (TrOLEDs) can be integrated into architectural glass windows, car windshields, divider panels, or lamps, thus enabling the creation of lighting objects with captivating and innovative designs, allowing natural light to pass through, since they are optically transparent when turned off. In order to achieve high-performance TrOLED, it is necessary to develop transparent electrodes with superior optical and electrical properties, to replace the opaque metal top electrodes that are commonly used in bottom-emitting OLEDs. Transparent conducting oxides (TCOs) are the most widely used transparent materials for bottom electrodes, and sputtering technology is the most common technique to deposit such materials. However, sputtering of high-quality TCO is not well suited for the fabrication of OLED top electrodes because it exposes the underlying organic layers to damages by the plasma emission of high-energy particles. In this study, the effects of sputter deposition of Indium Tin Oxide (ITO) on Tris(8-hydroxyquinoline)aluminum(III) (Alq3) OLED active layer have been investigated, to establish the best compromise between process conditions and ITO films electro-optical properties to reduce the damage induced by sputtering. Moreover, the impact of introducing a thin thermally evaporated calcium (Ca) layer, before ITO sputtering, has also been examined. In this case, Ca acts both as a protective layer for the underlying Alq3 and, at the same time, as a good electron injector for OLEDs
OLED devices optimization for lighting application
Full text link2015 - 2016In this work a potential new OLED application is presented: a large-area purple OLED for horticultural application, which combines red and blue light emissions in a unique device.
The main issue of this thesis is to demonstrate the effectiveness of the proposed OLED structure by using theoretical models created during the three years of the Ph.D. studies and applied to commercial materials.
The core of this dissertation is the third chapter, where the reader is brought to the optimization of the final purple OLED structure after several experiments, which confirm either the basic concepts explained in the two previous chapters, either a mathematical model for a fine-tuning of the blue emission layer.
Behind the proposed device architecture and material employed, there is the concept of “hybrid OLEDs with triplet harvesting”, where a proper combined use of fluorescent and phosphorescent emitting materials allows a theoretical internal quantum efficiency of 100%.
The last chapter is focused on the study and the realization of metal grids on the indium-tin-oxide (ITO), which is the most used material as transparent and conductive anode for the OLED devices.
Despite ITO owns good property of transmittance (transparency), because of its limited conductivity, a lateral voltage drop occurs, preventing a homogeneous emission when the dimensions of the devices exceeds few square centimetres.
To overcome this problem, it is presented a new mathematical model which, unlike the most established literature models do, takes into account both the electrical influence of the metal grid and that one of the ITO.
Finally, with a good agreement with the experimental data, the theoretical model is used to predict optical and electrical behaviour of different hexagonal metal grid on ITO.
It worth to underline that all the approaches implemented in this work to achieve a large-area purple OLED, have a general validity. Indeed, the entire know-how in this thesis it has been successfully used, in the last three years, to make several different OLED devices, different for colour emission, size and performances. [edited by Author]XV n.s. ( XXIX ciclo
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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