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Organic Light Emitting Devices (organic + light_emitting_device)
Selected AbstractsBook Review: Organic Light Emitting Devices.ADVANCED MATERIALS, Issue 8 2007By Klaus Mullen, Ullrich Scherf (Eds.). No abstract is available for this article. [source] Tris-Cyclometalated Iridium(III) Complexes of Carbazole(fluorenyl)pyridine Ligands: Synthesis, Redox and Photophysical Properties, and Electrophosphorescent Light-Emitting DiodesCHEMISTRY - A EUROPEAN JOURNAL, Issue 5 2007Sylvia Bettington Dr. Abstract Using ligands synthesized by Suzuki cross-coupling methodology, new phosphorescent homoleptic tris-cyclometalated complexes have been obtained, namely fac -[Ir(Cz-2-FlnPy)3] (1,d,f) and fac -[Ir(Cz-3-FlnPy)3] (2,d,f), which are solution-processible triplet emitters (Cz denotes N -hexylcarbazole, n is the number of 9,9,-dihexylfluorene (Fl) units (n=0,1,2) and Py is pyridine). In all cases, Py and Fl are substituted at the 2- and 2,7-positions, respectively, and Cz moieties are substituted by either Py or Fl at the 2- or 3-positions, in series 1 and 2, respectively. The oxidation potential of 1,d studied by cyclic voltammetry (=0.14,V, versus Ag/AgNO3, CH2Cl2) is less positive (i.e. raised HOMO level) compared to that of the isomer 2,d (=0.30,V), where the Cz-nitrogen is meta to the Ir center. Ligand-centered oxidations occur at more positive potentials, leading to 7+ oxidation states with good chemical reversibility and electrochemical quasi-reversibility, for example, for 2,f =0.45 (1e), 0.95 (3e), 1.24,V (3e). Striking differences are seen in the solution-state photophysical data between complexes [Ir(Cz-2-Py)3] (1,d) and [Ir(Cz-3-Py)3] (2,d), in which the Cz moiety is bonded directly to the metal center: for the latter there is an 85,nm blue-shift in emission, a decrease in the luminescence lifetime and an increase in the PLQY value. Organic light emitting devices were made by spin-coating using polyspirobifluorene:bis(triphenyl)diamine (PSBF:TAD) copolymer as host and the complexes 1,d or 2,d as dopants. Turn-on voltages are low (3,4,V). With 1,d orange light is emitted at ,max=590,nm with an EQE of 1.3,% (at 7.5,mA,cm,2) and an emission intensity (luminance) of 4354,cd,m,2 (at 267,mA,m,2). The green emission from 2,d devices (,max=500,nm) is due to the reduced electron-donating ability of the carbazole unit in 2,d. Recording the EL spectra of the 1,d device at 6,V (current density, 100,mA,cm,2) established that the time to half brightness was about 9,h under continuous operation with no change in the spectral profile, confirming the high chemical stability of the complex. [source] Fiber Shaped Light Emitting Device,ADVANCED MATERIALS, Issue 22 2007B. O'Connor A fiber based organic light emitting device (OLED) is demonstrated. Electrically, the device performs similarly to planar analogs, but unlike the planar devices, the fiber OLED exhibits an emission spectrum that is independent of the observation angle. This property may find application in OLED structures for display and lighting applications. The flexible fiber geometry potentially allows for new low cost manufacturing approaches. [source] Highly Emitting Neutral Dinuclear Rhenium Complexes as Phosphorescent Dopants for Electroluminescent DevicesADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Matteo Mauro Abstract A series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) is reported. These compounds, of general formula [Re2(µ -Cl)2(CO)6(µ -1,2-diazine)], contain diazines bearing alkyl groups in one or in both the , positions. Their electrochemical and photophysical properties are presented, as well as a combined density functional and time-dependent density functional study of their geometry, relative stability and electronic structure. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess high emission quantum yields (,,=,0.18,0.22 for the derivatives with disubstituted diazines). In butyronitrile glass, at 77,K, due to the charge transfer character of the lowest (emitting) excited state, strong blue shift of the emission is observed, accompanied by a strong increase in the lifetime values. The highest-performing emitting complex, containing cyclopentapyridazine as ligand, is tested in a polymer-based light-emitting device, with poly(9-vinylcarbazole) as matrix, as well as in a device obtained by vacuum sublimation of the complex in the 2,7-bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF) matrix. This represents the first example of devices obtained with a rhenium complex which can be sublimed and is solution processable. Furthermore, the emission is the bluest ever reported for electrogenerated luminescence for rhenium complexes. [source] The Influence of UV Irradiation on Ketonic Defect Emission in Fluorene-Based Copolymers,ADVANCED FUNCTIONAL MATERIALS, Issue 17 2008Horst Scheiber Abstract The influence of UV irradiation in inert atmosphere on the emission spectrum of fluorenone containing poly[9,9-bis(2-ethyl)hexylfluorene] (PF2/6) has been investigated by means of optical absorption, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. It is shown that a substantial reduction of green emission arising from ketonic defect sites can be achieved by irradiation of thin films with UV light. This is found to be accompanied by partial cross-linking of the films. FTIR measurements show no reduction of the C=O stretching mode upon irradiation, and, moreover, the degree of cross-linking does not scale with the relative fluorenone content (0.1, 0.5, and 5%). Therefore, the reduced emission intensity in the green spectral region is rather associated with the occurrence of interruptions in the polymer backbone, which reduce the effective conjugation length and subsequently inhibit the energy transfer onto the ketonic defect sites. The found results enabled us to build organic light emitting devices (OLEDs) that can be structured by selective illumination of the emitting layer with an intense UV light source. This method allows for the fabrication of rather efficient (2000,cd,m,2 at 7,V) two-color OLEDs. [source] High Definition Digital Fabrication of Active Organic Devices by Molecular Jet Printing,ADVANCED FUNCTIONAL MATERIALS, Issue 15 2007J. Chen Abstract We introduce a high resolution molecular jet (MoJet) printing technique for vacuum deposition of evaporated thin films and apply it to fabrication of 30,,m pixelated (800,ppi) molecular organic light emitting devices (OLEDs) based on aluminum tris(8-hydroxyquinoline) (Alq3) and fabrication of narrow channel (15,,m) organic field effect transistors (OFETs) with pentacene channel and silver contacts. Patterned printing of both organic and metal films is demonstrated, with the operating properties of MoJet-printed OLEDs and OFETs shown to be comparable to the performance of devices fabricated by conventional evaporative deposition through a metal stencil. We show that the MoJet printing technique is reconfigurable for digital fabrication of arbitrary patterns with multiple material sets and high print accuracy (of better than 5,,m), and scalable to fabrication on large area substrates. Analogous to the concept of "drop-on-demand" in Inkjet printing technology, MoJet printing is a "flux-on-demand" process and we show it capable of fabricating multi-layer stacked film structures, as needed for engineered organic devices. [source] Poly(methyl methacrylate) copolymers containing pendant carbazole and oxadiazole moieties for applications in single-layer organic light emitting devicesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2008David D. Evanoff Jr. Abstract Methyl methacrylate derived monomers functionalized with pendant carbazole and oxadiazole moieties were synthesized and could be copolymerized to form a random copolymer. The glass transition temperature of the copolymers could be predicted with a Fox equation and ranged from 140 to 191 °C. The photoluminescent characteristics of the copolymers, both in solution and in solid films, exhibited emission that was a combination of sharp and broad peaks, suggestive of monomeric and chromophore aggregation emission. These trends were also apparent in the electroluminescent response of the copolymers, where the appearance of an electromer emission was evident and was tentatively assigned to the carbazole moieties. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7882,7897, 2008 [source] Measuring carrier mobility in conventional multilayer organic light emitting devices by delayed exciton generationPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 5 2008S. Reineke Abstract The authors present an alternative method for the determination of the charge carrier mobility of organic thin films. In contrast to known methods like space charge limited current, field effect transistor and time of flight approaches, we determine the charge carrier mobility of a mixed film, serving as emission layer, within the conventional multilayer device architecture. We make use of a strong delayed generation feature in the electroluminescent decay, following a short voltage pump pulse in a time-resolved set-up. Taking into account the preferentially electron transporting properties of the film, the mobility of a N,N ,-di(naphthalen-2-yl)- N,N ,-diphenyl-benzidine (NPB):tris(1-phenylisoquinoline) iridium [Ir(piq)3] mixed film is found to be on the order of 10,5 cm2 (Vs),1. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Role of bathocuproine as hole-blocking and electron-transporting layer in organic light emitting devicesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010Reni Tomova Abstract In this paper we present our results concerning the role of 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproine, BCP) in OLED structures with emissive layer of Tris-(8-hydroxyquinoline) aluminum (Alq3). It is established that instead of the higher working voltage of devices with bathocuproine their current efficiency significantly increased. This higher efficiency indicates strong hole-blocking nature of bathocuproine (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||