Application In Organic Light-emitting Devices Research Articles

Highly phosphorescence iridium complexes and their application in organic light-emitting devices.

A new series of iridium(III) mixed ligand complexes TBA[Ir(ppy)(2)(CN)(2)] (1), TBA[Ir(ppy)(2)(NCS)(2)] (2), TBA[Ir(ppy)(2)(NCO)(2)] (3), and [Ir(ppy)(2)(acac)] (4) (ppy = 2-phenylpyridine; acac = acetoylacetonate, TBA = tetrabutylammonium cation) have been developed and fully characterized by UV-vis, emission, IR, NMR, and cyclic voltammetric studies. The lowest energy MLCT transitions are tuned from 463 to 494 nm by tuning the energy of the HOMO levels. These complexes show emission maxima in the blue, green, and yellow region of the visible spectrum and exhibit unprecedented phosphorescence quantum yields, 97 +/- 3% with an excited-state lifetimes of 1-3 micros in dichloromethane solution at 298 K. The near-unity quantum yields of these complexes are related to an increased energy gap between the triplet emitting state and the deactivating e(g) level that have been achieved by meticulous selection of ligands having strong ligand field strength. Organic light-emitting devices were fabricated using the complex 4 doped into a purified 4,4'-bis(carbazol-9-yl)biphenyl host exhibiting a maximum of the external quantum efficiencies of 13.2% and a power efficiency of 37 lm/W for the 9 mol % doped system.

Low moisture permeation measurement through polymer substrates for organic light emitting devices

Low permeation measurements through polymer substrates is very critical and there is no definite commercial method for measuring a water vapor transmission rate of 10 −6 g/m 2/day at 39 °C and 95% RH at atmospheric pressure. A novel moisture permeation measurement method and model was developed qualitatively and quantitatively with the ‘calcium degradation test’ method. It is well known that organic light emitting device structures and other active display materials degrade in the presence of oxygen and moisture. This method would be highly suitable for assessing ultra high barrier properties of polymer substrates for organic light emitting device applications.

Polynaphthalimide is a new polymer for organic electroluminescence devices

The electroluminescence of polyimide film made on the basis of naphthalimide derivative was observed for the first time. These polymers named polynaphthalimides are very thermally and radiation stable. The further development of various polynaphthalimides is perspective for application in organic light-emitting devices.

A Novel Yellow Fluorescent Dopant for High-Performance Organic Electroluminescent Devices

We have synthesized a novel yellow dopant (DCTP) for applications in organic light-emitting devices (OLEDs), by introducing a triphenylamine segment as a π electron donor and 4-(dicyanomethylene)-2-(tert-butyl)-4H-pyran moiety as a π electron acceptor to the molecular structure. The resultant dopant has a high fluorescent yield and a sterically well-hindered structure. Its photoluminescence in solution and electroluminescence have been studied. The DCTP-doped OLED with a structure of indium tin oxide/N,N‘-bis(3-methylphenyl)-N,N‘-diphenyl-1,1‘-biphenyl-4,4‘-diamine (TPD)/tris(8-quinolinolato)aluminum (Alq3):2 wt % DCTP/Alq3/Mg:Ag shows a bright yellow emission (chromaticity coordinates: x = 0.47; y = 0.51) and a brightness of 19 383 cd/m2 at a driving voltage of 20 V. The current efficiency of the device reaches 5.3 cd/A at a current density of 20 mA/cm2 and a voltage of 11 V.

X-ray photoelectron spectroscopy and atomic force microscopy investigation of stability mechanism of tris-(8-hydroxyquinoline) aluminum-based light-emitting devices

Stability is an essential issue in the application of organic light-emitting devices (OLEDs). We have investigated the indium tin oxide (ITO) surface for operated and unoperated OLEDs using x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The device structure consists of ITO/phenyl-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq3)/Mg:Ag with NPB thickness varied from 0 to 300 Å. The ITO surface was exposed by removing the organic and metal layers with dichloromethane, an organic solvent in which NPB and Alq3 are highly soluble. Electroluminescence characterization demonstrates that the NPB layer substantially enhanced the stability. XPS analysis shows that for the device made without NPB and after 90 h of operation, there exists an insoluble organic material on the ITO surface. This organic material is not observed on the ITO of unoperated devices. Lateral force AFM also shows a striking difference between the ITO surface of devices with and without NPB after operation. The XPS and AFM results suggest that the organic residue is the degradation product of Alq3 that acts as quenching sites at the ITO/Alq3 interface, which contribute to the early failure of the single-layer devices.

Achieving full-color organic light-emitting devices for lightweight, flat-panel displays

We review recent results in the field of organic light-emitting devices (OLED's), with particular attention to the application of organic light-emitting devices to ultra-lightweight, full color, flat-panel displays. We show that OLED brightness, efficiency, operating voltage, and lifetime is sufficient to compete with other flat-panel display technologies such as backlit liquid crystal displays. We describe a novel, tunable OLED consisting of vertically stacked, transparent light-emitting devices which can serve as a color-tunable element in high-resolution full-color display., In addition, the unique physical properties of organic thin films allow for flexible, conformable, or foldable displays which are unobtainable with conventional, inorganic semiconductor technologies.

Internal Field Distribution in Organic Light Emitting Diodes with Double Layer Structure

AbstractDouble layer organic light emitting devices (OLED) are constructed by evaporating tris(8 -hydroxy) quinoline aluminum (Alq3) on a spin cast thin film of a methyl substituted ladder type poly -para -phenylene (m -LPPP). A thick layer of Mg:Ag is used as the cathode material. These organic materials are very suitable for application in OLEDs both, as transporting materials as well as active layers. Alq3 predominantly transports electrons while m - LPPP is a conjugated polymer having higher hole mobilities. Due to these transport properties the formation and radiative recombination of the excitons in ITO/m -LPPP/Alq3/Mg:Ag devices occur close to the m -LPPP/Alq3 interface. We compare the device performance of OLEDs with varying Alq3 layer thickness (0, 50, 150, 300, 500Å) and constant m -LPPP layer thickness (900Å). A difference in the device parameters and performance as a function of the Alq3 layer thickness is observed. We analyze these results with respect to the internal electric field distribution of the double layer devices derived from electroabsorption measurements.