Organic light-emitting device with a mixed ligand 8-quinolinolato aluminium chelate as emitting and electron transporting material (original) (raw)
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New rare-earth quinolinate complexes for organic light-emitting devices
Thin Solid Films, 2013
Because of its thermal and morphological stability and optical and electrical properties, tris(8-hydroxyquinoline) aluminum (Alq 3 ) is one of the most widely used electron transporting materials in organic light-emitting devices (OLEDs). The search for substitutes for this compound constitutes an important field of research in organic electronics. We report on a study of a new rare-earth tetrakis 8-hydroxyquinoline complex. Synthesis of tris complexes with rare-earth metals and 8-hydroxyquinoline resulted in unstable compounds. However, the inclusion of an additional quinoline group stabilized these compounds. Li[RE(q) 4 ] (where RE=La 3+ , Lu 3+ and Y 3+ and q=8-hydroxyquinoline) were synthesized and then used as the electron-transporting and emitting layer in OLEDs. Thin films were deposited in a high-vacuum environment by thermal evaporation on quartz and silicon substrates. Optical characterization of the RE complexes revealed emission in the 510-525 nm range, the same as that observed for Alq 3 , while absorption was observed at wavelengths of 382 nm for the Y/La complexes and 388 nm for the Lu complex. The OLEDs were fabricated with an indium tin oxide layer (ITO) as the anode, (N,N′-bis (1-naphtyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine) NPB as the hole-transporting layer (25 nm), Li[RE(q) 4 ] as the electron-transporting and emitting layer (40 nm) and aluminum as the cathode (120 nm). The electroluminescence (EL) spectra showed a broad band from 520 to 540 nm and green-colored emission associated with the 8-hydroxyquinoline ligand. There was an interesting dependence of the maximum energy peak position and half-width of the emission band in the EL spectra on the atomic radius of the RE ion used. The best luminance for the OLEDs produced in this study was achieved with the Li[RE(q) 4 ] compound. The optical and electrical properties of this OLED were comparable to those of similar devices based on Alq 3 .
American Journal of Applied Sciences, 2010
ABSTRACT Problem statement: How the thickness of the tris (8-hydroxyquinolinato) Aluminum (Alq3) effect the optical and electrical properties of organic light emitting diode. Approach: The optimum thickness, photoluminescence and current-voltage characteristic of Alq3 layer on N, N-bis (inaphthyl)- N,N-diphenyl-1,1-biphenyl-4,4-diamine (55 nm) layer in Organic Light-Emitting Devices (OLED) structure are reported. Alq3 and NPB organic layers are used as Electron Transport Layer (ETL) and as Hole Transport Layer (HTL) in Organic Light-Emitting Devices (OLED). The thin layers of the NPB and Alq3 were prepared by thermal evaporation method. Results: The Alq3 layer was evaporated on the NPB layer for thickness ranging from 16 to 134 nm and photoluminescence and I-V characteristic were studied using fiber optics spectrophotometer (Ocean Optics- USB 2000 FLG) and current-voltage source (Keithley, model 2400). Conclusion: It was found that the Alq3 with 84 nm thicknesses gives the highest photoluminescence peak at 520 nm wavelengths, as well as the lowest turn on voltage of the device. The optical reflectance spectra for every sample were also reported.
In this study we investigated theoretically the electronic structure of [tris-(8-hidroxiquinolinolato) aluminum (III)-Alq 3 , solvation properties of the electroluminescent Alq 3 organic liquids such as methanol and ethanol in order to understand the dependence the variation of system environments, improving the operation of conveyors films in electroluminescent devices of the type OLED (Organic Light-Emitting Diodes), and finally investigated the mechanism of Alq 3 in the electron transport applying a low electrical current in the molecule and current curves showing the -voltage characteristic of the device. The simulation method consists of applying a classic dynamic methodology and subsequently with a quantum treatment to plot the electronic spectra of the layers of Alq 3 by ZINDO/S method. In the electrical properties of transport we use the Green function method coupled nonequilibrium density functional theory (DFT) inferring that the ramifications outer rings corresponding to the Alq 3 would terminals for electronic transfer. Our results showed that the average absorption spectra of Alq 3 for solvation in solutions undergoes a minimum deviation with changing environment, being in good agreement with the experimental results from the literature, and the IV curves confirmed the behavior of the diode device, corroborating the senses as more relevant to the terminals in Alq 3 to have a satisfactory transport electronics.
Mei Yee Lim, Wan Mahmood Mat Yunus, Zainal Abidin Talib, Anuar Kassim
The optical properties of N,N’-bis (Inaphthyl)N,N’-diphenyl-1,1’-biphenyl-4,4’-diamine (NPB) and tris (8-hydroxyquinolinato) aluminum (Alq3) organic materials used as hole transport and electron transport layers in organic light-emitting devices (OLED) have been investigated. The NPB and Alq3 layers were prepared using thermal evaporation method. The results show that the energy band gap of Alq3 is thickness independence while the energy band gap of NPB decreases with the increasing of sample thickness. For the case of photoluminescence the Alq3 with thickness of 84 nm shows the highest relative intensity peak at 510 nm.
Journal of Materials Science: Materials in Electronics, 2020
Organic light-emitting diodes (OLEDs) play a key role in modern display devices and systems. A highly desirable material for fabricating OLEDs is tris(8hydroxyquinoline)aluminum (Alq 3). In this work, a highly efficient OLED based on dysprosium (Dy)-incorporated Alq 3 (Alq 3-Dy) was fabricated. The fabricated OLED had four layers, namely, those of indium tin oxide (ITO), N, N 0-Di(1naphthyl)-N, N 0-diphenyl-(1,1 0-biphenyl)-4,4 0-diamine (NPB), Alq 3-Dy, and aluminum (Al). The ITO and Al layers were used as electrodes, while the NPB was selected as a hole transport layer. All the layers were deposited sequentially on a glass substrate. The surface morphologies of these layers clarified that the materials were deposited as nanosphere particles. The OLED performance showed significant improvement in terms of the operating voltage, current efficiency, and luminance of the fabricated Alq 3-Dy OLED compared with that of the pure Alq 3 OLED device. The luminance value was significantly enhanced from approximately 250 cd/m 2 for the pure Alq 3 OLED to approximately 5000 cd/m 2 for the Alq 3-Dy OLED. Moreover, the electroluminescence (EL) intensity of the Alq 3-Dy OLED was 20 times higher than that of the Alq 3 OLED. These findings may have a significant impact on the fabrication of the OLEDs and display devices.
Journal of Physics and Chemistry of Solids, 2008
We have designed, synthesized and characterized a novel compound comprising red fluorescent material, (2Z,2 0 Z)-3,3 0 -[4,4 00bis(dimethylamino)-1,1 0 :4 0 ,1 00 -terphenyl-2 0 ,5 0 -diyl]bis(2-phenylacrylonitrile) (ABCV-P), which prevented concentration quenching in nondoped, organic light-emitting diodes (OLEDs). 4-(Dicyanomethylene)-2-methyl-6-(julolidine-4-yl-vinyl)-4H-pyran (DCM2), which is used as a red dopant in OLEDs, is vulnerable to concentration quenching in the solid state due to its planar and polar molecular structure. To investigate the effect of the molecular structure on the surface morphology of thin solid films, which affects solid-state fluorescence and electroluminescence (EL), a thin solid film of ABCV-P was compared with that of DCM2 by atomic force microscopy (AFM) analysis. The AFM analysis showed that the thin solid film of ABCV-P exhibited badly crystalline or amorphous-like surface morphology, in contrast to that of DCM2. The photoluminescence (PL) of the thin solid film of ABCV-P peaked at 596 nm, while no such peak was observed for DCM2. A device with the structure of ITO/NPB/ABCV-P/BCP/Alq 3 /Liq/Al showed an EL spectrum which peaked at 586.5 nm at 8 V, with a maximum luminance of 3320 cd/m 2 at 687 mA/cm 2 and a maximum luminous efficiency of 0.703 cd/A at 7.7 mA/cm 2 . In comparison, the OLED device with DCM2 as a host-emitter did not exhibit any red EL due to concentration quenching in the solid state. r
Thin Solid Films, 2010
a b s t r a c t on electron injection and device performance in organic light-emitting diodes based on tris-(8hydroxyquinoline) aluminum, were investigated systematically. The insertion of the buffer layers at the organic/cathode interface not only reduced the operating voltage, but also enhanced the luminance and efficiency, which is attributed to the improvement of electron injection efficiency. It was found that the efficiency of the electron injection was closely related to the inherent properties of the buffer layer, such as its melting point (MP) and dielectric constant (ε), as well as with the buffer layer's interface with the metallic electrode through the effective work function (WF). Low MP, low ε and low WF values result in an effective improvement in the injection of the electrons, and thus to the device performance. The electroluminescent performance was further improved by the introduction of calcium between the buffer layer and the aluminum electrode.