Shintaro Enomoto

A host material consisting of a phosphinic amide directly linked donor–acceptor structure for efficient blue phosphorescent organic light-emitting diodes

A host material with a high triplet excited-state energy level and a deep HOMO energy level has been developed by directly linking the donor and acceptor units through a phosphinic amide. Phosphorescent organic light-emitting diodes containing this material and a deep-blue dopant achieved an external quantum efficiency of 19.7%.

25.4: High-Brightness Large-Area White OLED Fabricated by Meniscus Printing Process

We demonstrated high-brightness large-area, white organic light-emitting diode (OLED) consisting of printing-processed organic semiconductor layers. Meniscus printing process was applied to the substrate with 2 μm-high stripe-shape auxiliary electrodes. The OLED panel showed white emission all over the whole emitting area of 58 mm × 52 mm, high average luminance of 10,000 cd/m2, luminance uniformity of 40 %, and high luminous flux of 95 lm.

P-73: Reflective Color LCD Composed of Stacked Films of Encapsulated Liquid Crystal (SFELIC)

A reflective color liquid crystal display (LCD), which dose not consume power for backlighting, is a key device for portable information equipment. A novel structure for three-layered guest-host (GH) liquid crystal displays (LCDs) has been proposed. The structure, called stacked films of encapsulated liquid crystal (SFELIC), has no intermediate substrates, and is expected to realize low cost and high brightness while eliminating parallax.

67.3: Electrochemical Reaction Display with Dual Reflective and Emissive Modes

We have developed an electrochemical reaction display (ECRD) that can be operated in dual reflective and emissive modes in an entire pixel area of a single device. The ECRD utilizes electrochromic (EC) and electrogenerated chemiluminescence (ECL) reactions. These two electrochemical reactions can be controlled independently by adding a luminescent molecule to a liquid electrolyte of an EC cell with three electrodes. In the reflective mode, the ECRD cell exhibits high reflectance (47%) and high contrast ratio (6:1). In the emissive mode, the cell can show luminescent moving images because of the fast response time (10 ms).

Effect of horizontal molecular orientation on triplet-exciton diffusion in amorphous organic films

Triplet harvesting is a candidate technology for highly efficient and long-life white OLEDs, where green or red phosphorescent emitters are activated by the triplet-excitons diffused from blue fluorescent emitters. We examined two oxadiazole-based electron transport materials with different horizontal molecular orientation as a triplet-exciton diffusion layer (TDL) in triplet-harvesting OLEDs. The device characteristics and the transient electroluminescent analyses of the red phosphorescent emitter showed that the triplet-exciton diffusion was more effective in the highly oriented TDL. The results are ascribed to the strong orbital overlap between the oriented molecules, which provides rapid electron exchange (Dexter energy transfer) in the TDL.

Large Area Microencapsulated Reflective Guest-Host Liquid Crystal Displays and Their Applications

We have developed reflective liquid crystal displays using microencapsulated guest-host liquid crystals, whose size was sufficiently large for viewing documents. A high-brightness image can be realized because there is no need for polarizers. Easy fabrication processes, consisting of screen-printing of microencapsulated liquid crystal and film adhesion, have enabled the realization of thinner and lighter cell structures. It has been confirmed that the display is tolerant of the pressures to which it would be subject in actual use. The optimization of fabrication processes has enabled the realization of reflectance uniformity in the display area and reduction of the driving voltage. Our developed display is suitable for portable information systems, such as electronic book applications.

Reflective color LCD composed of stacked films of encapsulated liquid crystal (SFELIC)

A reflective color liquid-crystal display (LCD), which does not consume power for backlighting, is a key device for portable information equipment. A novel structure for three-layered guest-host (GH-LCDs) has been proposed. The structure, called stacked films of encapsulated liquid crystal (SFELIC), has no intermediate substrates, and is expected to realize low cost and high luminance while eliminating parallax.

Fluorinated Poly( N -vinylcarbazole) Host for Triplet Energy Confinement on Phosphorescent Emitter in Organic Light-emitting Diodes

Fluorinated carbazoles as host materials have been investigated for highly efficient organic light emitting diodes (OLEDs). By molecular orbital calculations, we found that fluorinations at position 2, 4, 5 and 7 of carbazole ring were effective for widening HOMO-LUMO energy gap. The energy gaps of our synthesized 2,7-difluorocarbazole (F2-Cz) and 2,4,5,7-tetrafluorocarbazole (F4-Cz), were estimated to be 3.71 eV and 3.87 eV by the absorption spectra, respectively. These energy gaps were higher than that of the non-substituted carbazole (Cz, 3.59 eV). We synthesized poly( N -vinyl-2,7-difluorocarbazole) (F2-PVK) and poly( N -vinyl-2,4,5,7-tetrafluorocarbazole) (F4-PVK) as solution processable polymer host materials. However, the F4-PVK was found to be an unsolved polymer. The F2-PVK could be compared with non substituted poly( N -vinylcarbazole) (PVK) in OLEDs. The emission layer (EML) contained iridium(III) bis [(4,6-di-fluorophenyl)-pyridinato- N,C2 ′] picolinate (FIrpic) as a blue phosphorescent dopant, and iridium(III) bis [2-(9,9-dihexylfluorenyl)-1-pyridine] acetylacetonate as a yellow dopant. The white OLED with the F2-PVK showed 1.4 times higher luminous current efficiency (24 cd/A) than the PVK (17 cd/A). These data show that the excitation energy is confined on dopants by using fluorinated polymer host material with higher T1 corresponding to wider HOMO-LUMO energy gap.