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Yuichi HINO Hirotake KAJII Yutaka OHMORI
We have demonstrated improvement in the efficiency of TDAPB-based OLEDs. The external quantum efficiency of 8.2% and a power efficiency of 17.3 lm/W were achieved. The results suggest that using the starburst small-molecule TDAPB allows for easy fabrication and is effective for achieving high efficiencies in simple device structures.
Yutaka OHMORI Norio TADA Yoshitaka KUROSAKA Hiroshi UETA Takumi SAWATANI Akihiko FUJII Katsumi YOSHINO
Multicolor light emitting diodes (LEDs) which emit red (R), green (G) and blue (B) light have been realized by stacking a two-color emission part on a single-color emission part. The former part consists of two emissive layers of red and blue light, which can be selected by changing the polarity of applied field. The latter part consists of a single-color emission part which emits green light. The emission from the diode in the whole visible spectral range can be modulated by the combination of applying various voltages to the two-color and to the single-color emission parts, separately.
Yutaka OHMORI Chikayoshi MORISHIMA Akihiko FUJII Katsumi YOSHINO
Electrical and optical properties of organic multilayer structure have been investigated. Two types of current-voltage characteristics have been found for thin multilayer structure of organic films. Optical property and its application for electroluminescent diode have been presented. The diode characteristics have been discussed in terms of energy band scheme.
Keiichi KANETO Kazuhiro KUDO Yutaka OHMORI Mitsuyoshi ONODA Mitsumasa IWAMOTO
Recent technologies of organic film devices are reviewed. New technologies of fabrication and characterization of organic thin films, electro-mechanical conversion materials, and applications for electrical and optical devices are discussed. In this review paper, especially organic light emitting diodes, tunneling junctions using polyimide Langmuir-Blodgett films, tunneling spectroscopy and high-density recording, plastic actuators using conducting polymers, molecular self-assembly process for fabricating organic thin film devices are reviewed.
Hirotake KAJII Masato ISE Hitoshi TANAKA Takahiro OHTOMO Yutaka OHMORI
The effects of the gate dielectrics on ambipolar transport in top-gate-type polymer light-emitting transistors with single-layer and bilayer gate dielectrics are investigated. Hole field-effect mobility is dependent on the dielectric constant of the gate dielectric onto the active layer. Hole transport of devices is affected by the dipolar disorder in the first gate dielectric layer on the active layer. Electron threshold voltage tends to decrease with increasing the total stacked gate capacitance.
Hirotake KAJII Hiroshi OKUYA Shohei FUKUDA Akinori SAKAKIBARA Yutaka OHMORI
Organic field-effect transistors (OFETs) based on a composite with the same thiophene backbone were fabricated by spin coating using an annealing solution of poly(3-hexylthiophene) (PAT6) and α, ω-dihexylsexithiophene (DH-6T). The morphology of grains on the non-octadecyltrichlorosilane (OTS) treated and OTS treated gate insulators is granular and tube-like, respectively. The different morphologies of the OFETs with non-OTS treated and OTS-treated gate insulators result in the improvement of field-effect mobility. In the case of poly(ethylene naphthalate) substrate, an OFET with an 89 wt% DH-6T composite corresponding to two molecules of DH-6T per hexylthiophene repeating unit had a carrier mobility of 0.019 cm2/Vs.
Hirotake KAJII Takahisa TSUKAGAWA Takayuki TANEDA Yutaka OHMORI
The optical pulses of 50 MHz has been obtained from an organic light emitting diode (OLED) based on the Alq3 emissive layer with the active area of 0.01 mm2. We demonstrate that the OLEDs can be applied to fields of optical communication as the electro-optical conversion device for transmitting the signals of moving picture.
Takumi SAWATANI Yutaka OHMORI Katsumi YOSHINO
We demonstrate unique dye-doping method to realize organic light emitting diodes (OLED) with high efficiency, high brightness and pure red emission. In this study, we used 5,10,15,20 tetraphenyl -21H,23H-porphine (TPP) as emitting dopant into 8-hydroxyquinoline aluminum (Alq3) emissive layer. To improve turn-on voltage and emission characteristics, a sufficient amount of 4-(dicyano methylene) -2-methyl -6-(p-dimethyl aminostyryl) -4H-pyran (DCM) was added to the TPP doped Alq3 emissive layer. The mechanisms and the emission characteristics of the co-doped EL device are discussed using energy band diagram of the materials used in the device.
Yuichi HINO Hirotake KAJII Yutaka OHMORI
We investigated luminescent properties in combination of red emissive europium complex of tris(dibenzoylmethane)-mono(4,7-dimethylphenanthroline)europium(III) [Eu(dbm)3phen] and blue phosphorescent molecule of bis[(4,6-difluorophenyl)-pyridinato-N,C2'] (picolinate) iridium (III) (FIrpic) doped in poly(N-vinyl-carbazole) (PVK). A sharp red emission from Eu(dbm)3phen was observed in photoluminescence (PL) measurement, whereas, in the case of electroluminescence (EL), emission from FIrpic and Eu compound were observed. The difference of the PL and EL spectra indicates that different energy transfer processes between Eu(dbm)3phen and FIrpic are suggested.
Tatsunari HAMASAKI Taichiro MORIMUNE Hirotake KAJII Yutaka OHMORI
The characteristics of violet-sensitive organic photodetectors (OPDs) utilizing polyalkylfluorene and triplet materials have been studied as a host and a dopant material, respectively. For the photo absorption layer, poly(9,9-dioctylfluorene) [PFO] and a phosphorescent iridium complex (Iridium (III) bis(2-(4,6-difluorophenyl)pyridinato-N,C2) [FIrpic] or Iridium (III) bis(2-(2'-benzothienyl)pyridinato-N,C3')(acetyl-acetonate) [(btp)2Ir(acac)]) were used as a host and a dopant material, respectively. PFO: (btp)2Ir(acac) device showed less photocurrent than PFO device because (btp)2Ir(acac) enhances recombination of the photo generated carriers in the photo absorption layer. On the other hand, PFO : FIrpic device showed larger photocurrent than PFO device due to triplet energy transfer from FIrpic to PFO. A cutoff frequency of 20 MHz was observed using a sinusoidal modulated violet laser light illumination under the reverse bias of 8 V.
Mitsumasa IWAMOTO Yutaka OHMORI
Hirotake KAJII Toshinari KOJIMA Yutaka OHMORI
High luminance and high speed response with the cut-off frequency of more than 50 MHz in multilayer polyfluorene-based light-emitting diodes with an interlayer were achieved. We realized multilayer polyfluorene-based light-emitting diodes for frequency response up to 100 MHz.
Mitsuyoshi ONODA Hiroshi NAKAYAMA Yutaka OHMORI Katsumi YOSHINO
Optical recording has been performed successfully by the preirradiation of light upon the precursor of poly (arylene vinylene) conducting polymers such as poly (p-phenylene vinylene) (PPV) and poly (1,4-naphthalene vinylene) (PNV) and subsequent thermal treatment. The effect has been tentatively interpreted in terms of the deterioration of the irradiated area of the precursor polymer in which polymerization is suppressed. Furthermore, an orange electroluminescent (EL) diode utilizing PNV has been demonstrated for the first time and the EL properties of PNV are discussed in comparison with those of EL diode utilizing PPV. The EL emission of these two devices are discussed in terms of radiative recombination of the singlet polaron exciton formed by the injection of electrons and holes, the difference of effective conjugation length and the interchain transfer of polaron excitons.
Hirotake KAJII Kazuya TAKAHASHI Yuichi HINO Yutaka OHMORI
The luminance of about 10,000 cd/m2 at an applied voltage of 9.2 V and the external emission efficiency 5.5 cd/A at an injection current density of 50 mA/cm2 have been obtained from an organic light emitting diode (OLED) using starburst molecule doped with 5,6,11,12-tetraphenylnaphthacene fabricated by wet-processing. We demonstrate that the OLEDs fabricated by wet-processing can be applied to fields of short range optical communication as the electro-optical conversion device for transmitting the signals of moving picture.