Sukekazu Aratani

Complete Suppression of Color Shift in In-plane Switching Mode Liquid Crystal Displays with a Multidomain Structure Obtained by Unidirectional Rubbing

Complete suppression of color shift in in-plane switching mode liquid crystal displays (LCDs) has been realized. The LCDs have a multidomain structure obtained by unidirectional rubbing and use of zigzag electrodes. The design concept and performance of the devices are described in this paper.

Optical characterization of the in-plane switching effect utilizing multidomain structures

Color shift and gray scale reversal for very large viewing angles are analyzed theoretically for in-plane switching. It follows that the color shift depends on the change of the effective birefringence dΔn, whereas gray scale reversal depends on the effective angle between the polarizers and the liquid-crystal director angle. Experimental results confirmed the theory that small gray levels result in a larger color shift. Likewise, the viewing angles in which a gray scale reversal occurs, correlate with the theory. To counter these drawbacks, two multidomain structures are proposed, neither of which requires additional orientation processes. With these multidomain structures, color shift was suppressed and no gray scale reversal was observed. However, the multidomain structures reduce maximum transmission, the extent of which depends on the type and design of the structure.

Effect of Molecular Orbital Distributions on Charge Transport Properties of Polymers Doped with Triphenylamine Derivatives

The hole drift mobilities of polymers doped with triphenylamine derivatives including heterocyclic groups have been measured and the effect of molecular orbital distributions of triphenylamine derivatives on the charge transport properties has been studied. The temperature dependence of the mobilities of polymers doped with two kinds of triphenylamine derivatives has been analyzed using the disorder formalism presented by Bassler and co-workers[H. Bassler, Phys. Status Solidi B 175(1993) 15.] and it has been found that highest occupied molecular orbital (HOMO) distribution of the triphenylamine derivatives has little effect on the diagonal and off-diagonal disorder but has a large effect on the disorder-free mobility in this formalism.

Collimated Light Source Using Patterned Organic Light-Emitting Diodes and Microlens

We developed for the first time a collimated organic light-emitting diode (OLED) light source using a patterned OLED and a microlens. The structure of the collimated OLED light source was designed by conventional ray-tracking simulation. We demonstrated that the collimated OLED light source enhanced the luminance of a liquid crystal display (LCD) with a low aperture ratio by a factor of more than two compared with a conventional OLED light source, which was not patterned. The collimated OLED light source with the patterned OLED and microlens is thus very effective for achieving a highly efficient LCD with OLED backlight.

Unusual Voltage-Holding Ratio Characteristics Using In-Plane Switching of Nematic Liquid Crystals

Unusual characteristics of the voltage-holding ratio were found when using in-plane switching of homogeneously oriented nematic liquid crystals. Even when employing liquid crystals with much lower resistivity than is applicable to the conventional active matrix driving technique, voltage-holding ratio characteristics were higher than those in conventional electric fields applied along the direction perpendicular to the substrate plane. The unusual holding ratio characteristics were attributed to the electric field direction being approximately parallel to the substrate plane.

Effect of Electronic States of Triphenylamine Derivatives on Their Charge Transport Properties

The hole drift mobilities of polymers doped with triphenylamine derivatives have been measured and the effect of the electronic states of triphenylamine derivatives on the charge transport properties has been studied. The HOMO (highest occupied molecular orbital) distribution strongly affects the charge transport properties and it was found that when the triphenylamine part had more HOMO distribution, the mobility increased. Moreover, 2-[p-di(p-tolyl)aminostyryl]-4-methylthiazole was found as a new charge transport material having rather high drift mobility.

10.5L: Late‐News Paper: High Efficiency and High Operational Stability Top‐Emitting OLEDs

We have succeeded in developing top-emitting OLEDs with high efficiency and high operational stability using the V2O5 buffer layer to suppress the damage from the bombardment of highly energetic particles and the degradation of the organic materials of the OLEDs by active oxygen in the sputtering process.

47.4L: Late‐News Paper: High‐efficiency White Organic Light‐emitting Diodes with a Two‐stack Multi‐photon Emission Structure

We have demonstrated a novel white OLED with two vertically stacked emission units. The first emission unit employs a blue fluorescent emitter and the second one uses green and red phosphorescent emitters. The device architecture achieves low-driving voltage and the combination of the emitters without deterioration in luminous efficiency.

Enhancement of blue‐light‐emission properties for OLED displays by using a polarized light‐recycling structure

— The blue-light-emission properties of organic light-emitting-diode (OLED) displays must be enhanced to meet the requirements for color purity and luminous efficiency because few blue-light-emitting materials meet these requirements. This is particularly true for polymeric and phosphorescent light-emitting materials. To attain the required purity and efficiency, a polarized-light-recycling structure for blue light that is called a blue enhanced circular polarizer (BECP) has been developed. The principle of the structure and the fabricated prototype device is described and it is shown that the structure increases blue-light intensity and color purity, improves efficiency, provides a wide color gamut, and limits ambient-light reflection.

34.4L: Late‐News Paper: Light Out‐Coupling Enhancement of OLEDs by a Polarized Light Recycling Structure

We have realized a blue light out-coupling enhancement of OLEDs using a polarized light recycling structure. This structure gives increased blue light intensity and color purity, as well as high efficiency and a wide color gamut while suppressing the increase of ambient light reflection.