Search results for "ELECTROLUMINESCENCE"
showing 10 items of 128 documents
Host–guest blue light-emitting electrochemical cells
2014
Carbazole, a commonly used hole-transporter for organic electronics, has been modified with an imidazolium cation and a hexafluorophosphate counter-anion to give an ionic hole-transporter. It has been applied as one of the hosts in a host–guest blue light-emitting electrochemical cell (LEC) with the neutral blue emitter FIrPic. We have obtained efficient and bright blue LECs with an electroluminescence maximum at 474 nm and efficacy of 5 cd A−1 at a luminance of 420 cd m−2, thereby demonstrating the potential of the ionic organic charge-transporters and of the host–guest architecture for LECs.
Engineering Charge Injection Interfaces in Hybrid Light-Emitting Electrochemical Cells
2014
Light-emitting electrochemical cells (LECs) consists of a thin film of an ionic organic semiconductor sandwiched between two electrodes. Because of the large density of ions, LECs are often reported to perform independently on the electrodes work function. Here we use metal oxides as charge injection layers and demonstrate that, although electroluminescence is observed independently of the electrodes used, the device performances are strongly dependent on the choice of the interface materials. Relying on metal oxide charge injection layers, such hybrid devices are of interest for real lighting applications and could pave the way for new efficient, stable, low-cost lighting sources.
Bis(N-naphthyl-N-phenylamino)benzophenones as exciton-modulating materials for white TADF OLEDs with separated charge and exciton recombination zones
2022
Abstract Organic semiconductors were employed as exciton modulators, blue emitters, hole-transporting materials and hosts with resonant-appropriate singlet and triplet energies for efficient and stable white organic light emitting diodes (OLEDs). Two 4,4'-bis(N-naphthyl-N-phenylamino)benzophenones were synthesized using isomeric N-naphthyl-N-phenylamines as the donors and benzophenone as the acceptor moiety. Molecular design of new compounds allowed to obtain required combination of properties, i.e. blue prompt fluorescence in solid state with singlet energies close to those of the selected blue emitter exhibiting thermally activated delayed fluorescence (TADF), low triplet energies of 2.32…
Improving the efficiency of light-emitting diode based on a thiophene polymer containing a cyano group
2007
Abstract We report on the overall improvement of a single layer organic light-emitting diode device based on poly{[3-hethylthiophene]-co-3-[2-( p -cyano-phenoxy)ethyl]thiophene} or namely PTOPhCN. This polymer was recently developed by adding a cyano group as a side-chain substituent of the thiophenic backbone onto the main polymer chain and showed promising results for light-emitting diode devices. Using an improved device layout, bright red electroluminescence was obtained at 4 V and showed a luminance of about 400 cd/m 2 at 8 V with current densities in the order of 6000 A/m 2 .
Electroluminescence of (Pb0.91La0.09)(Zr0.65Ti0.35)O3 relaxor ceramics
2013
Abstract Lanthanum doped lead zirconate titanate (PLZT) relaxor ceramics with (Pb 0.91 La 0.09 )(Zr 0.65 Ti 0.35 )O 3 composition exhibit a repolarization induced by electroluminescence (EL) with a pronounced discrete character of emission. It is established that this behavior is related to the reorientation of nanodimensional polar regions in a strong pulsed electric field in the vicinity of a smeared phase transition. The time and temperature dependences of the EL intensity are studied.
Peripheral halo-functionalization in [Cu(N^N)(P^P)]+ emitters: influence on the performances of light-emitting electrochemical cells
2016
A series of heteroleptic [Cu(N^N)(P^P)][PF6] complexes is described in which P^P = bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) and N^N = 4,4′-diphenyl-6,6′-dimethyl-2,2′-bipyridine substituted in the 4-position of the phenyl groups with atom X (N^N = 1 has X = F, 2 has X = Cl, 3 has X = Br, 4 has X = I; the benchmark N^N ligand with X = H is 5). These complexes have been characterized by multinuclear NMR spectroscopy, mass spectrometry, elemental analyses and cyclic voltammetry; representative single crystal structures are also reported. The solution absorption spectra are characterized by high energy bands (arising from ligand-c…
White Light-Emitting Electrochemical Cells Based on the Langmuir–Blodgett Technique
2014
Light-emitting electrochemical cells (LECs) showing a white emission have been prepared with Langmuir-Blodgett (LB) films of the metallosurfactant bis[2-(2,4-difluorophenyl)pyridine][2-(1-hexadecyl-1H-1,2,3-triazol-4-yl)pyridine]iridium(III) chloride (1), which work with an air-stable Al electrode. They were prepared by depositing a LB film of 1 on top of a layer of poly(N,N'-diphenyl-N,N'-bis(4-hexylphenyl)-[1,1'-biphenyl]-4,4'-diamine (pTPD) spin-coated on indium tin oxide (ITO). The white color of the electroluminescence of the device contrasts with the blue color of the photoluminescence of 1 in solution and within the LB films. Furthermore, the crystal structure of 1 is reported togeth…
Fine‐Tuning of Photophysical and Electronic Properties of Materials for Photonic Devices Through Remote Functionalization
2012
We report four new iridium(III) complexes of the type [Ir(ppy)2(N?N)][PF6] in which N?N is a 4,6-diphenyl-2,2`-bipyridine and the 4-phenyl ring is substituted at either the para or meta positions [4-Me, N?N = 1; 4-Br, N?N = 2; 3,5-Br2, N?N = 3; 3,5-(C6H4-4-NPh2)2, N?N = 4]. The complexes have been fully characterized, and single-crystal diffraction analyses of [Ir(ppy)2(N?N)][PF6] (N?N = 13) confirmed that each [Ir(ppy)2(N?N)]+ cation exhibits face-to-face p-stacking between the pendant phenyl substituent of the N?N ligand and the cyclometallated phenyl ring of an adjacent [ppy] ligand. In solution, the complexes are short-lived emitters; the emission maxima for [Ir(ppy)2(1)][PF6], [Ir(ppy)…
Extended liquid-crystalline oligofluorenes with photo- and electroluminescence
2010
In this paper we report the synthesis and characterization of a series of low-molecular weight light-emitting molecules based on short oligofluorene cores, from one to three 9,9-dioctylfluorene units, elongated at the 2- and 7-positions by means of promesogenic units. The effect of this structural modification on the mesomorphic properties, as well as on the optical and electrochemical properties, is studied. The possibility of using these molecules as emitters in light-emitting diodes (LEDs) and polarized photoluminescent layers has been explored.
Near-Quantitative Internal Quantum Efficiency in a Light-Emitting Electrochemical Cell
2008
A green-light-emitting iridium(III) complex was prepared that has a photoluminescence quantum yield in a thin-film configuration of almost unity. When used in a simple solid-state single-layer light-emitting electrochemical cell, it yielded an external quantum efficiency of nearly 15% and a power efficiency of 38 Lm/W. We argue that these high external efficiencies are only possible if near-quantitative internal electron-to-photon conversion occurs. This shows that the limiting factor for the efficiency of these devices is the photoluminescence quantum yield in a solid film configuration. The observed efficiencies show the prospect of these simple electroluminescent devices for lighting and…