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Device Efficiency (device + efficiency)

Distribution by Scientific Domains

Polymers and Materials Science	75%

Distribution within Polymers and Materials Science

General & Introductory Materials Science	54%
Polymer Science & Technology General	44%

Selected Abstracts

Optimization of opto-electronic property and device efficiency of polyfluorenes by tuning structure and morphology

POLYMER INTERNATIONAL, Issue 5 2006
Peng Chen
Abstract Polyfluorene-based oligomers and polymers (PFs) have been studied intensively as active materials for organic optoelectronic devices. In this review, the optimization of the opto-electronic property and device efficiency of polyfluorenes in the field of light-emitting diodes (LEDs) and photovoltaic cells (PVs) by tuning structure and morphology are summarized in terms of two typical modification techniques: copolymerization and blending. The relationships between molecular structures, thin film morphologies, opto-electronic properties and device efficiencies are discussed, and some recent progress in LEDs and PVs is simultaneously reviewed. After the introduction, the basic knowledge of molecular structures and properties of polyfluorene homopolymers is presented as a background for a better understanding of their great potential for opto-electronic applications. Immediately after this, three different opinions on the origin of low-energy emission band at 520,540 nm in polyfluorene-based LEDs are addressed. Rod,coil block copolymers and alternative copolymers are focused on in the next section, which are a vivid embodiment of controlling supramolecular structures and tailoring molecular structures, respectively. In particular, various supramolecular architectures induced by altering coil blocks are carefully discussed. Recent work that shows great improvement in opto-electronic properties or device performance by blending or doping is also addressed. Additionally, the progress of understanding concerning the mechanisms of exciton dynamics is briefly referred to. Copyright © 2006 Society of Chemical Industry [source]

Water-Soluble Polyfluorenes as an Interfacial Layer Leading to Cathode-Independent High Performance of Organic Solar Cells

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Seung-Hwan Oh
Abstract Novel poly[(9,9-bis((6,-(N,N,N -trimethylammonium)hexyl)-2,7-fluorene)- alt -(9,9-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-9-fluorene)) dibromide (WPF-6-oxy-F) and poly[(9,9-bis((6,-(N,N,N -trimethylammonium)hexyl)-2,7-fluorene)- alt -(9,9-bis(2-(2-methoxyethoxy)ethyl)-fluorene)] dibromide (WPF-oxy-F) compounds are developed and the use of these water-soluble polymers as an interfacial layer for low-cost poly(3-hexylthiophene):phenyl-C61 butyric acid methyl ester (P3HT:PCBM) organic solar cells (OSCs) is investigated. When WPF-oxy-F or WPF-6-oxy-F is simply inserted between the active layer and the cathode as an interfacial dipole layer by spin-coating water-soluble polyfluorenes, the open-circuit voltage (Voc), fill factor (FF), and power-conversion efficiency (PCE) of photovoltaic cells with high work-function metal cathodes, such as Al, Ag, Au, and Cu, dramatically increases. For example, when WPF-6-oxy-F is used with Al, Ag, Au, or Cu, regardless of the work-function of the metal cathode, the Voc is 0.64, 0.64, 0.58, and 0.63,V, respectively, approaching the original value of the P3HT:PCBM system because of the formation of large interfacial dipoles through a reduction of the metal work-function. In particular, introducing WPF-6-oxy-F into a low-cost Cu cathode dramatically enhanced the device efficiency from 0.8% to 3.36%. [source]

Red-Emitting Polyfluorenes Grafted with Quinoline-Based Iridium Complex: "Simple Polymeric Chain, Unexpected High Efficiency"

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
Zhihua Ma
Abstract A series of red-light emitting electrophosphorescent polyfluorenes (PFs) with varying content of a quinoline-based iridium complex, (PPQ)2Ir(acac) (bis(2,4-diphenylquinolyl-N,C2,) iridium(acetylacetonate)), in the side chain are synthesized by Suzuki polycondensation. Because of the efficient Förster energy transfer from the PF main chain to (PPQ)2Ir(acac) and direct charge trapping on the complex, the electroluminescent emission from PF is nearly completely quenched, even though the amount of iridium complex incorporated into the polymers is as low as 1,mol %. Based on a single-layer device configuration, a luminous efficiency of up to 5.0,cd A,1 with a luminance of 2000,cd m,2 and Commission Internationale de L'Eclairage coordinates of (0.63, 0.35) (x, y) is realized, which is far superior to that of previously reported red-light emitting PFs containing benzothiazole- and isoquinoline-based iridium complexes. This result is beyond expectations, especially when considering that the simple polymeric chain involved has no additional charge-transporting moieties. Noticeably, the device efficiency remains as high as 4.2,cd A,1 with a luminance of 4000,cd m,2 even at current densities of 100,mA cm,2. Further optimization of the device configuration by incorporating an additional electron-injection layer leads to improved efficiencies of 8.3 and 7.5,cd A,1 at luminances of 100 and 1000,cd m,2, respectively. This state-of-the-art performance indicates that covalently attaching quinoline-based iridium complexes to a PF backbone is a simple and effective strategy to develop high-efficiency red-light emitting electrophosphorescent polymers. [source]

Polymer Photovoltaic Cells Based on Solution-Processable Graphene and P3HT

ADVANCED FUNCTIONAL MATERIALS, Issue 6 2009
Qian Liu
Abstract A soluble graphene, which has a one-atom thickness and a two-dimensional structure, is blended with poly(3-hexylthiophene) (P3HT) and used as the active layer in bulk heterojunction (BHJ) polymer photovoltaic cells. Adding graphene to the P3HT induces a great quenching of the photoluminescence of the P3HT, indicating a strong electron/energy transfer from the P3HT to the graphene. In the photovoltaic devices with an ITO/PEDOT:PSS/P3HT:graphene/LiF/Al structure, the device efficiency increases first and then decreases with the increase in the graphene content. The device containing only 10,wt % of graphene shows the best performance with a power conversion efficiency of 1.1%, an open-circuit voltage of 0.72,V, a short-circuit current density of 4.0,mA cm,2, and a fill factor of 0.38 under simulated AM1.5G conditions at 100,mW cm,2 after an annealing treatment at 160,°C for 10,min. The annealing treatment at the appropriate temperature (160,°C, for example) greatly improves the device performance; however, an annealing at overgenerous conditions such as at 210,°C results in a decrease in the device efficiency (0.57%). The morphology investigation shows that better performance can be obtained with a moderate content of graphene, which keeps good dispersion and interconnection. The functionalized graphene, which is cheap, easily prepared, stable, and inert against the ambient conditions, is expected to be a competitive candidate for the acceptor material in organic photovoltaic applications. [source]

Highly Efficient and Color-Stable Deep-Blue Organic Light-Emitting Diodes Based on a Solution-Processible Dendrimer

ADVANCED MATERIALS, Issue 47 2009
Lei Wang
A color-stable blue organic light-emitting diode is obtained utilizing a solution-processible fluorescent , -conjugated dendrimerG0 (see image), with a maximum luminance efficiency of 5.3,cd A,1. Efficient green, red, and white OLEDs are also demonstrated by doping G0 with phosphorescent dyes. Combining high device efficiency with solution processibility, G0 becomes one of the best blue-emitting materials for fabricating flat-panel displays and white-light lighting panels via solution processing. [source]

Efficient Polymer Solar Cells Fabricated by Simple Brush Painting,

ADVANCED MATERIALS, Issue 24 2007
S.-S. Kim
We demonstrate a brushing technique as a promising method for the mass production of efficient and flexible solar cells even on a non-flat surface such as roofing tiles. Higher device efficiency could be obtained compared to the spin-coated devices, resulting from the improved organization of polymer chains and domains induced by more effective application of shear stress to the polymer chains during the brushing process. [source]

Phenylene vinylene-based electroluminescent polymers with electron transport block in the main chain

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2006
Honghao Sun
Abstract We report a new route for the design of soluble phenylene vinylene (PV) based electroluminescent polymers bearing electron-deficient oxadizole (OXD) and triazole (TZ) moieties in the main chains with the aryloxy linkage. Both series of the PV-based polymers were prepared by Wittig reaction. By properly adjusting the OXD and/or TZ content through copolymerization, we can achieve an enhanced balance of hole- and electron injections, such that the device efficiency is significantly improved. Light-emitting diodes fabricated from P1, P2, P3, P4, P5, P6, and P7 with the configuration of Indium,Tin Oxide (ITO)/Poly (styrene sulfonic acid) doped poly (ethylenedioxythiophene) (PEDOT)/polymer/Ca/Al, emit bright green light with the maximum peak around 500 nm. For the device using the optimal polymer (P4) as emitting layer, a maximum brightness of 1300 cd/m2 at 20 V and a maximum luminance efficiency of 0.325 cd/A can be obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3469,3478, 2006 [source]

Optimization of opto-electronic property and device efficiency of polyfluorenes by tuning structure and morphology

Study of base series resistance losses in single and double emitter silicon solar cells through simulations and experiments

PROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 7 2008
K. Kotsovos
Abstract This work focuses on base series resistance influence on the performance of single and double emitter rear point contact silicon solar cells. This study is performed through measurements on experimental devices with different rear contact sizes and spacings, which were designed and fabricated using standard silicon integrated circuit technology, while the results were compared with simulation data based on a 3D model developed at our institute. Simulation and experimental results show that the series resistance of the double junction structure is significantly lower compared to the single junction equivalent. In addition, it was demonstrated that the operation of both junctions under slightly different voltages improves device efficiency. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Ovum Pick-up in Sheep: a Comparison between Different Aspiration Devices for Optimal Oocyte Retrieval

REPRODUCTION IN DOMESTIC ANIMALS, Issue 2 2006
C Rodríguez
Contents In vivo ovum pick-up (OPU) in sheep may be improved with a proper choice of aspiration elements (needle and tubing) and aspiration vacuum pressure. In the present study, two experiments were carried out. In Expt 1, visible follicles in ovaries of slaughtered ewes (treated separately according to their diameters: small <3 mm, medium 3,5 mm and large >5 mm) were aspirated using different combinations of the three studied factors such as aspiration flow rate (10, 20, 30, 40 and 50 ml water/min), needle gauge (18 and 20 G) and tubing inner diameter (1, 2 or 3 mm internal diameter). In Expt 2, a study with two 18 G needles of different lengths (18 G: 82 mm; 18 GL: 600 mm) was carried out, using ovaries obtained post-mortem, and performing in vivo laparoscopic follicular aspiration on ewes. We considered good quality oocytes as those with both complete compact cumulus and a homogeneous cytoplasm. Recovery rate, proportion of good quality oocytes (good quality oocytes/100 oocytes recovered) and overall efficiency (good quality oocytes/100 follicles aspirated) were noted. In Expt 1, aspiration flow rate affect remarkable proportion of good quality oocytes (69.5%, 50.5%, 44.8%, 36.5% and 28.3% for flows from 10 to 50 ml/min respectively, p < 0.05). Needle gauge did not affect aspiration device efficiency. Thin and intermediate tubings were more effective (overall efficiency rates: 34.9%, 32.3% and 28.1% for 1, 2 and 3 mm respectively, p < 0.05). Follicle size did not affect recovery rate, but proportion of good quality oocytes was higher for large (77.9%) and medium (64.4%) follicles (p < 0.05). Finally, some combinations of the aspiration device showed greater effectiveness. In Expt 2, needle length did not influence recovery rate, but good quality oocytes rate was significantly modified both post-mortem and in vivo (good quality rate for 18 G vs 18 GL needles: 69.5% vs 47.7% and 58.1% vs 25.4%, post-mortem and in vivo respectively, p < 0.05). We conclude that low-aspiration flow rates (10 and 20 ml/min) with thin or intermediate tubings (1 and 2 mm), and any short needle (18 G or 20 G) are the most adequate aspiration factors for OPU in sheep. [source]

,-Conjugated Dendrimers as Stable Pure-Blue Emissive Materials: Photophysical, Electrochemical, and Electroluminescent Properties

CHEMISTRY - AN ASIAN JOURNAL, Issue 4 2009
Yang Jiang
Abstract Bigger, stronger, better: A family of giant ,-conjugated dendrimers has been developed as pure-blue active materials for organic light-emitting diodes. The dendrimer-generation number has little effect on the photophysical, electrochemical, and EL properties, and device efficiency of G0 and G1. The preliminary OLED devices achieve pure-blue color with stable CIE chromaticity coordinates (0.16, 0.08) for both G0 and G1. A family of giant ,-conjugated dendrimers has been developed as pure-blue active materials for organic light-emitting diodes (OLEDs). The investigation of their photophysical properties indicates that G0 and G1 exhibit almost the same absorption and PL spectra in dilute solutions and in thin films. The steric hindrance of the bulky dendrimers effectively prevents strong intermolecular interaction in the solid state, which effectively improves the emission spectral stability. Preliminary OLEDs fabricated with the configuration of ITO/PEDOT:PSS/PVK/dendrimer/TPBI/Ba/Al achieve a pure-blue emission with stable CIE chromaticity coordinates (0.16, 0.08) for both G0 and G1. These results indicate that G0 and G1 are promising blue-light emitting materials with good stability. Such strategy provides us a platform to achieve pure-blue emitting dendrimer-like materials with high efficiency for use as OLEDs. [source]