Takeo Wakimoto

Multilayered organic electroluminescent device using a novel starburst molecule, 4,4’,4‘‐tris(3‐methylphenylphenylamino)triphenylamine, as a hole transport material

A novel π‐conjugated starburst molecule, 4,4’,4‘‐tris(3‐methylphenylphenylamino)triphenylamine (m‐MTDATA), which forms a stable amorphous glass, functions as an excellent hole transport material for organic electroluminescent devices. An electroluminescent device consisting of double hole transport layers of m‐MTDATA and 4,4’‐bis(3‐methylphenylphenylamino)biphenyl and an emitting layer of tris(8‐quinolinolato)aluminum exhibits a high luminance efficiency and significant durability.

Organic EL cells using alkaline metal compounds as electron injection materials

Organic electroluminescent (EL) devices with multilayer structure were fabricated using alkaline metal compounds as the electron injection materials. We found that the EL cells using the alkaline metal compounds reduce the driving voltage and increase the quantum EL efficiency. In addition, these cells are made with good reproducibility compared with the cells using aluminum and lithium alloy cathode.

Starburst molecules based on π-electron systems as materials for organic electroluminescent devices

Abstract Novel families of starburst molecules based on π-electron systems, which readily form morphologically and thermally stable, uniform amorphous films by vacuum deposition, have been found to function as excellent materials for organic electroluminescent (EL) devices. The multilayer organic EL devices consisting of double hole-transport layers and an emitting layer have been shown to exhibit high performances.

An organic LED display exhibiting pure RGB colors

Abstract A full color 5.2-in. 1/4 video graphics array (VGA) passive-matrix organic light emitting diode (OLED) display has been developed. The display features 320 (×3)×240 pixels with an equivalent pixel size of 0.33×0.33 mm 2 , white peak luminance of over 150 cd/m 2 , and power consumption of 6 W. It uses a cathode patterning method with electrically insulated cathode separators and an RGB emitters selective deposition method with a high accuracy mask moving system. Furthermore, we have achieved pure RGB colors as well as high luminance from the cells by applying the optical interference effects. The display can display high resolution video rate pictures with virtually the same quality as a CRT can offer.

Stability characteristics of quinacridone and coumarin molecules as guest dopants in the organic LEDs

Abstract During stability testing of organic light-emitting diodes (LEDs), a large amount of current (charge) injected into the LED cells raises the cell temperature quite a bit. The morphology of the organic thin films may have changed and formed the excimer and exciplex between different molecules. To keep the excimer and exciplex from forming during the driving test, the organic molecules should give steric hindrance by bulky substituents so that they do not move in the films. Moreover, the molecular structures should not have reactive chemical bonds. A cell doped with quinazoline or quinacridone, with bulky substituents at the imino group side in the Alq host, has a longer operational half-lifetime than that of a cell with quinacridone doping. A cell doped with coumarin derivative, which has no imino and carbonyl, also has a longer operational half-lifetime than that of a cell doped with coumarin with imino and carbonyl.

Progress in organic multilayer electroluminescent devices

Survey of dye materials for the emission layer in the multilayer organic electroluminescent (EL) device is discussed in terms of emission color and fluorescent efficiency. Organic semiconductors for the electron or the hole transport layer in the EL device are proposed for preparing stable homogeneous thin layer. Requirement of accomplishing the confinement of the singlet excitons generated by the recombinations of injected electrons and holes is discussed by using three layer EL devices with extremely thin bimolecular emission layer. Then the emphasis is laid on the size effects in three layer EL device with double heterojunctions on the spontaneous emission. Variations of the intensity and pattern of outer emission through semitransparent ITO glass substrate with the spacing between the emission layer and the metallic electrode are discussed theoretically and experimentally. And variation of the fluorescent lifetime or the radiative decay rate with the spacing is also discussed theoretically and experimentally.

Organic Electroluminescent Devices Using Novel Starburst Molecules, 1,3,5-Tris[4-(3-Methylphenyl-Phenylamino)Phenyl]Benzene And 4,4′,4″-Tris(3-Methyl-Phenylphenylamino)Triphenylamine, as Hole-Transport Materials

Abstract Organic electroluminescent devices using novel starburst molecules, 1,3,5-tris[4-(3-methylphenylphenylamino)phenyl]benzene (m-MTDAPB) and 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), as hole-transport materials and tris(8-quinolinolate)aluminium (Alqs) as an emitting material were fabricated and their performance characteristics examined. The starburst molecules were found to function as excellent hole-transport materials. The ITO/m-MTDATA(300A)/m-MTDAPB(200A)/Alq3(500A)/MgAl device exhibited a luminance of ca. 17,000 cd m−2 at a driving voltage of 16 V and a luminous efficiency of 1.9 1m W−1 at a luminance of 300 cd m−2.

Organic LED full‐color passive‐matrix display

— A full-color 5.2-inch 1/4-VGA passive-matrix organic LED display has been developed, adopting selective deposition for the different emitting materials. The display features 320 (×3) × 240 pixels with an equivalent pixel size of 0.33 × 0.33 mm, white peak luminance of over 150 cd/m2, and power consumption of 6 W.

Organic EL cells with high luminous efficiency

The guest-emitter doped system has been reported to give a bright electroluminescence (EL). By doping the emitter layer with highly fluorescent dyes, emission colors can be changed and the brightness is also increased. Low work function metals are generally used as a cathode to ensure easier electron injection into organic materials and are expected to reduce driving voltage and increase quantum efficiency for EL devices. We have developed a high luminance dot-matrix display using an organic EL device for the first time.

Dot‐matrix display using organic light‐emitting diodes

— A dot-matrix display with 256 × 64 pixels with a pixel size of 0.34 × 0.30 mm in size, a luminance of 100 cd/m2, and a contrast ratio of 100:1 or better has been developed using organic LED devices. The display provides high luminance, high visibility, and wide viewing angle.