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Organic Light Emitting Diodes (organic + light_emitting_diode)
Selected AbstractsThermally Activated Delayed Fluorescence from Sn4+,Porphyrin Complexes and Their Application to Organic Light Emitting Diodes , A Novel Mechanism for ElectroluminescenceADVANCED MATERIALS, Issue 47 2009Ayataka Endo Electroluminescence based on TADF, that is, thermally activated delayed fluorescence, is demonstrated in Sn4+,porphyrin complexes. On excitation by a short electrical pulse, prompt and delayed electroluminescence components were clearly observed. The delayed component was composed of both TADF and phosphorescence (see figure), and the TADF component significantly increased with increasing temperature. [source] Polythiophene-Fullerene Based Photodetectors: Tuning of Spectral Response and Application in Photoluminescence Based (Bio)Chemical SensorsADVANCED MATERIALS, Issue 37 2010Kanwar S. Nalwa A photoluminescence (PL)-based oxygen and glucose sensor utilizing inorganic or organic light emitting diode as the light source, and polythiophene:fullerene type bulk-heterojunction devices as photodetectors, for both intensity and decay-time based monitoring of the sensing element's PL. The sensing element is based on the oxygen-sensitive dye Pt-octaethylporphyrin embedded in a polystyrene matrix. [source] Integrated fluorescence sensor based on ring-shaped organic photodiodesPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7 2010Bernhard Lamprecht Abstract We demonstrate a novel sensor type, which is based on the monolithic integration of luminescent optical sensor spots together with ring-shaped thin-film organic photodiodes on one substrate. The organic photodiodes serve as integrated fluorescence detectors, simplifying the detection system by minimizing the number of required optical components. The proposed concept enables filter-less discrimination between excitation light and generated fluorescence light. The functionality of the concept is demonstrated by an integrated oxygen sensor, exhibiting excellent performance. The sensor spots are excited by an assembled organic light emitting diode. The integrated optical sensor platform is suitable for the parallel detection of multiple parameters. Sensor schemes for the analytical parameters carbon dioxide, temperature and ammonia, are proposed. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] CMP properties and fabrication of OLED using MEH-PPVPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2008Woo-Sun Lee Abstract The interface between the electrode and organic layer in organic light emitting diode (OLED) has been reported as an important factor to influence the electrical and luminescent properties. Indium tin oxide (ITO) is commonly used as the anode material. ITO thin film has been deposited on glass substrate by radio frequency (RF) magnetron sputtering. And it was used as an anode contact to fabricate OLED device. The OLED devices with ITO/MEH-PPV [2-methoxy-5-(2-ethylhexyloxy)-p-phenylenevinylene]/Al configuration were fabricated by thermal evaporation and spin coating, respectively. We investigated the electrical, structural and optical properties of ITO thin film, which was measured using the methods of atomic force microscope (AFM), field-emission scanning electron microscope (FESEM) and ultraviolet,visible (UV,VIS) spectrophotometer. The interface property between ITO thin film and MEH-PPV was improved as the surface of ITO thin film was smoothed and photoluminescence (PL) intensity was increased in the 680 nm range. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multifunctional Crosslinkable Iridium Complexes as Hole Transporting/Electron Blocking and Emitting Materials for Solution-Processed Multilayer Organic Light-Emitting DiodesADVANCED FUNCTIONAL MATERIALS, Issue 7 2009Biwu Ma Abstract Here, a new series of crosslinkable heteroleptic iridium (III) complexes for use in solution processed phosphorescent organic light emitting diodes (OLEDs) is reported. These iridium compounds have the general formula of (PPZ-VB)2Ir(C,N), where PPZ-VB is phenylpyrazole (PPZ) vinyl benzyl (VB) ether; and the C,N ligands represent a family of four different cyclometallating ligands including 1-phenylpyrazolyl (PPZ) (1), 2-(4,6-difluorophenyl)pyridyl (DFPPY) (2), 2-(p-tolyl)pyridyl (TPY) (3), and 2-phenylquinolyl (PQ) (4). With the incorporation of two crosslinkable VB ether groups, these compounds can be fully crosslinked after heating at 180,°C for 30,min. The crosslinked films exhibit excellent solvent resistance and film smoothness which enables fabrication of high-performance multilayer OLEDs by sequential solution processing of multiple layers. Furthermore, the photophysical properties of these compounds can be easily controlled by simply changing the cyclometallating C,N ligand in order to tune the triplet energy within the range of 3.0,2.2,eV. This diversity makes these materials not only suitable for use in hole transporting and electron blocking but also as emissive layers of several colors. Therefore, these compounds are applied as effective materials for all-solution processed OLEDs with (PPZ-VB)2IrPPZ (1) acting as hole transporting and electron blocking layer and host material, as well as three other compounds, (PPZ-VB)2IrDFPPY (2), (PPZ-VB)2IrTPY(3), and (PPZ-VB)2IrPQ(4), used as crosslinkable phosphorescent emitters. [source] Hole Injection in a Model Fluorene,Triarylamine CopolymerADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Hon Hang Fong Abstract Recent developments in synthesis and purification have yielded conjugated polymers with hole mobilities exceeding 0.01,cm2 V,1 s,1. Essential to harvesting the potential of these materials in organic light emitting diodes (OLEDs) is the identification of suitable ohmic contacts. Using a model fluorene copolymer that shows high-mobility, non-dispersive hole transport, it is demonstrated that electrodes commonly used as anodes in OLEDs are very poor hole injectors. Injection from Au and indium tin oxide anodes is limited by energy barriers of 0.75 and 0.65,eV, respectively, and the injected current is found to be temperature independent,a prediction that was not reproduced by the leading injection model for disordered organic semiconductors. Injection from a poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) anode, on the other hand, is found to become less efficient with electric field, a behavior which is currently not understood. In thinner poly[(9,9,-dioctylfluorenyl-2,7-diyl)- co -(4,4,-(N -(4- sec -butyl))diphenylamine)] films, which are of relevance to OLEDs, ohmic losses on the PEDOT:PSS layer are found to limit the flow of current. These results illustrate the opportunity to further improve the performance of OLEDs as well as the challenge posed by high mobility conjugated polymers for the design of hole injection layers. [source] Harvesting Triplet Excitons from Fluorescent Blue Emitters in White Organic Light-Emitting Diodes,ADVANCED MATERIALS, Issue 21 2007G. Schwartz A novel concept for white organic light emitting diodes (OLEDs) enabling the utilization of all electrically generated excitons for light generation is introduced. The key feature is a fluorescent blue emitter with high triplet energy, rendering it possible to harvest its triplet excitons by letting them diffuse to an orange phosphorescent iridium complex. [source] Synthesis and properties of nitrogen-linked poly(2,7-carbazole)s as hole-transport material for organic light emitting diodesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 15 2009Tsuyoshi Michinobu Abstract A novel class of carbazole polymers, nitrogen-linked poly(2,7-carbazole)s, was synthesized by polycondensation between two bifunctional monomers using the palladium-catalyzed amination reaction. The polymers were characterized by 1H NMR, Infrared, Gel permeation chromatography, and MALDI-TOF MS and it was revealed that the combination of the monomer structures is important for producing high molecular weight polymers. Thermal analysis indicated a good thermal stability with high glass transition temperatures, e.g., 138 °C for the higher molecular weight polymer P2. To pursue the application possibilities of these polymers, their optical properties and energy levels were investigated by UV-Vis absorption and fluorescence spectra as well as their electrochemical characteristics. Although the blue light emission was indeed observed for all polymers in solution, the quantum yields were very low and the solid films were not fluorescent. On the other hand, the HOMO levels of the polymers estimated from the onset potentials for the first oxidation in the solid thin films were relatively high in the range of ,5.12 to ,5.20 eV. Therefore, light emitting diodes employing these polymers as a hole-transport layer and iridium(III) complex as a triplet emitter were fabricated. The device of the nitrogen-linked poly(2,7-carbazole) P3 with p,p,-biphenyl spacer, which has a higher HOMO level and a higher molecular weight, showed a much better performance than the device of P2 with m -phenylene spacer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3880,3891, 2009 [source] On the improvement of the electroluminescent signal of organic light-emitting diodes by the presence of an ultrathin metal layer at the interface organic/ITOPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2008J. C. Bernède Under DOI 10.1002/pssa.200723206 erroneously a paper was published online in January 2008 which already had been published elsewhere. Please find this paper, entitled "On the improvement of the electroluminescent signal of organic light emitting diodes by the presence of an ultra-thin metal layer at the interface organic/ITO" by J. C. Bernède, F. Martinez, G. Neculqueo, and L. Cattin under DOI 10.1002/pssr.200701217, published in phys. stat. sol. (RRL) 2, No. 1, 10,12 (2008). (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Anomalous current,voltage characteristics of thin polymer filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2003V. A. Kolesnikov Abstract In this paper we have investigated organic light emitting diodes with such electroluminescent materials as aromatic polyimide, poly,N-vinylcarbazole (PVK) and dye doped PVK. N-type current,voltage characteristics with negative differential resistance for the thin polymeric and organic films are analyzed. No reasonable explanation has been provided for this phenomenon until now. Here we suggest that a polymer(organic)/metal interface containing various inhomogeneities and metal spikes is responsible for this effect. We detect also the black-body radiation, whose temperature exceeds both the melting point and the sublimation temperature of the metal of the electrode. We suppose that the current density through the spike in any cases is large enough to cause the explosion of the tip of the spike and the detected radiation has the hot plasma origin. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pulsed electrically detected magnetic resonance in organic semiconductorsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009C. Boehme Abstract Carbon-based materials have an intrinsically weak spin,orbit coupling which imposes spin selection rules on many electronic transitions. The spin degree of freedom of electrons and nuclei can therefore play a crucial role in the electronic and optical properties of these materials. Spin-selection rules can be studied via magnetic resonance techniques such as electron,spin resonance and optically detected magnetic resonance as well as electrically detected magnetic resonance (EDMR). The latter has progressed in recent years to a degree where the observation of coherent spin motion via current detection has become possible, providing experimental access to many new insights into the role that paramagnetic centers play for conductivity and photoconductivity. While mostly applied to inorganic semiconductor materials such as silicon, this new, often called pulsed-(p) EDMR spectroscopy, has much potential for organic (carbon-based) semiconductors. In this study, progress on the development of pEDMR spectroscopy on carbon-based materials is reviewed. Insights into materials properties that can be gained from pEDMR experiments are explained and limitations are discussed. Experimental data on radiative polaron-pair recombination in poly[2-methoxy-5-(20-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) organic light emitting diodes (OLEDs) are shown, revealing that under operating conditions the driving current of the device can be modulated by spin-Rabi nutation of the polaron spin within the charge carrier pairs. From this experimental data it becomes clear that for polaron pairs, the precursor states during exciton formation, exchange interaction is not the predominant influence on the observed pEDMR spectra. [source] | |||||||||||||