Hitoshi Nakada

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.

Optical and electrical characteristics of organic light-emitting diodes with two-dimensional photonic crystals in organic/electrode layers

Efficient light extraction is a critical issue for improving the overall efficiency of organic light-emitting diodes (OLEDs). Improvements in OLED efficiency are studied via the introduction of photonic crystal (PC) layers, which are expected to enable versatile control of photons. We fabricate two-dimensional PC structures in organic and electrode layers, in which most light is confined, to extract the light in the waveguide mode. Improvements in OLED efficiency of 20 and 130% are observed in spectrally integrated intensity and the peak intensity of forward-propagating light, respectively, in comparison with samples without PCs. As the thickness of the organic layer is partially reduced, lower operating voltages are found not to degrade light-extraction efficiency. We can expect further improvement in the overall OLED efficiency by optimizing PC structure.

Reduction of operating voltage in organic light-emitting diode by corrugated photonic crystal structure

A reduction of the operating voltage is achieved for an organic light-emitting diode containing a corrugated photonic crystal structure fabricated by the etching of an indium-tin-oxide anode layer. This is due to a partial reduction in the thickness of the organic layer. The light extraction efficiency can be also improved due to the diffraction of confined light by the photonic crystal effect. The voltage reduction is demonstrated in combination with an improvement in the luminance efficiency at constant current for the fabricated device.

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.

21.1: Invited Paper: 3-inch Full-color OLED Display using a Plastic Substrate

We developed a full-color Organic Light Emitting Diode (OLED) display on a plastic substrate. The display area is a 3- inch diagonal area with 160 × RGB × 120 pixels. Silicon oxynitride (SiON) was used as a moisture barrier film on the substrate and silicon nitride (SiN) as a passivation film on the device. The display was approximately 0.2 mm thick, weighted approximately 3 g, and it was bendable.

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.

Micropatterning method for the cathode of the organic electroluminescent device

A unique method of micropatterning in the order of microns for an organic electroluminescent (OEL) device has been developed. The method consists of a cathode separator with a reverse tapered or a T-shaped cross section which is formed prior to the deposition of organic layers and metal cathodes. By introducing the cathode separator, a high-resolution OEL display panel with gaps of less than 30 µ m between pixels has been fabricated.

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.

Organic LED Full Color Passive-Matrix Display

A full color 5.2 inch 1/4VGA 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 mm2 white peak luminance of over 150 cd/m2 and power consumption of 6 W.