Publishing type：Research paper (scientific journal)  

© 2020 The Institute of Electrical Engineers of Japan. To investigate the breakdown mechanism in oil/PB composite insulation systems applied to power transformers, we have measured the electric field in partial discharge occurrence by the application of lightning impulse voltage using the electric field measurement system by electro-optical Kerr effect. It has confirmed that the system has sufficient time response for the measurement of the electric field during lightning impulse application. In the oil/PB composite insulation system, which has multi oil gaps, we could have confirmed the increase of the electric field of the other gaps when the partial discharge occurred in one of the oil gaps. Furthermore, we have confirmed that the obtained optical phase shift is similar to estimated value by electric field simulation.

DOI： 10.1541/ieejfms.140.325

Scopus

researchmap

Publishing type：Research paper (scientific journal)  

© 2019 The Institute of Electrical Engineers of Japan. Electro-optical method is one of methods to measure the electric field in dielectric liquids. In this method, the change of the light intensity due to the applied electric field must be measured. It is well known that dielectric liquids move with flowing under high voltage application. The intensity data might include some error by the liquid disturbance. In this paper, we describe about the effectiveness of the measurement system improved in order to measure the electric field strength in a transformer oil, for the measurement of the strength in liquid moving with flowing.

DOI： 10.1541/ieejfms.139.406

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Institute of Electrical Engineers of Japan  

© 2018 The Institute of Electrical Engineers of Japan. We have studied the electrical treeing generated in silicone gel used as an encapsulant for power electronics modules. The treeing which consist of bubbles and strings was named Pearl-chain-type treeing. Under AC voltage application, the bubble vibrated with repeating expansion and shrinkage. We have obtained new insight that the expansion of the bubble at polarity inversion was very important for the development of the tree.

DOI： 10.1541/ieejias.138.758

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical Engineers of Japan  

Silicone gels have been used as an encapsulation for power electronics modules. We investigated electric treeing in silicone gel under AC voltage. The trees in silicone gels consist of two parts: bubble and straight part. This type of tree is called pearl-chain type tree. The tree vibrates under AC voltage and its frequency of vibration was twice of the applied voltage. The diameter of bubble or the shape of whole tree evaluated the vibrating volume of tree. The large expanded tree/bubble and small expanded tree/bubble alternately appeared. The pearlchain type tree was observed under the voltage of rectangle wave. The inception voltage of tree under rectangle voltage was lower than the sine wave. The dependence of the growth patterns of the trees on the frequency of the applied voltage was investigated. At low frequencies (10 mHz ∼ 10 Hz), a bubble appeared at the tip of needle electrode, and a simple tree grew at 10 Hz. Trees had many small branches at 350 and 400 Hz and did not appear at frequencies over 450 Hz.

DOI： 10.23919/ISEIM.2017.8166592

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

In order to clarify breakdown mechanisms in insulation oil / pressboard composite dielectric system, it is effective to measure the electric field distributions. We have investigated the electric field distribution in transformer oil using Kerr electrooptic effect. At first, Kerr constant of the transformer oil was measured using the optical system. The constant was determined to be 2.0×10-15[m/V2]. Next, we measured the electric field in transformer oil in AC electric field in the order of milli-seconds. In order to reduce the error due to the fluctuation of light intensity of the laser, we used the improved optical system. As a result, we have been able to be confirmed that the change of light intensity when AC voltage application was followed to the principle of Kerr effect. In addition, as compared with the result measured by the conventional system, the result could be improved by the new system. Thus, we have been able to confirm that time series electric field measurement on the order of milli-seconds in transformer oil under AC voltage by using optical system based on Kerr effect. In the future, electric field measurement will be performed when partial discharge occurs by applying AC high voltage or pulse high voltage in insulation oil / pressboard composite dielectric system. The electric field distribution before and after the partial discharge will be measured and the breakdown mechanism will be investigated by based on the result.

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

A gel is used as the encapsulant of a power device. But there are a lot of uncertain points about the electrical properties of the gel. We have investigated the time series measurement of electric field distributions in propylene carbonate that was a dielectric liquid with large Kerr constant. The propylene carbonate dissolves polymethyl methacrylate resin and becomes gelatinous. It was considered that the relevance between the electrical properties of the gel and the liquid might become clear, if temporal change of the electric field strength could be measured in this gel. So, in this paper, we studied that the electric field strength could be measured in the gel using Kerr effect.

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人 電気学会  

© 2017 The Institute of Electrical Engineers of Japan. The development of electrical tree is one factor that the breakdown occur in solid insulator. So, the study concerning the tree has been proceeded. When the silicone rubber gel made by changing the degree of cross-linking agent was used as a sample, the tree named pearl-chain-type was generated. The pearl-chain-type tree consisted of two parts: string and bubble. Branching occurred at bubble parts. In this study, the pattern of pearl-chain-type tree was observed under different frequency of applied voltage using a high speed camera. Main branche and side branch was also considered.

DOI： 10.1541/ieejfms.137.215

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical Engineers of Japan  

Silicone gels have been used as an encapsulant of power electronics modules. We investigated electric treeing in silicone gel under AC voltage. The growth patterns of the trees depended on the frequency of the applied voltage. At low frequencies (10 mHz to 10Hz), a bubble appeared at the tip of needle electrode, and a simple tree grew at 10Hz. Trees had many small branches at 350 and 400 Hz and did not appear at frequencies over 450 Hz.

DOI： 10.1541/ieejias.137.458

Scopus

researchmap

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical Engineers of Japan  

A gel, which has characteristics of both a solid and a liquid is called a "soft material", is widely used in various industrial fields. But there are a lot of uncertain points about the electrical properties of the gel. In order to understand the growth mechanism of pearl-chain-type electrical trees in a polymer gel, and investigate about the relationship between the liquids and gels for the high electric field phenomena, the electric field distribution must be measured in the gel. This paper reports on the measurement of the electric field strength in a certain gel using Kerr effect. It is interesting that Kerr constant of the gel depend on the weight percent of a solvent.

DOI： 10.1541/ieejeiss.136.1420

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report that the photocurrent generation of a titanyl phthalocyanine (TiOPc) layer in heterojunction photovoltaic cells is strongly dependent on the crystalline phase of the TiOPc layer. Vacuum-deposited TiOPc films with an amorphous phase were changed into mixed crystalline films with two or three crystalline phases, Phase I and Phase II or Phase Y, by solvent vapor treatment with various solvents, which is confirmed from the ultraviolet-visible absorption spectra and X-ray diffraction patterns of solvent-vapor-treated TiOPc films. From the incident photon to current conversion efficiency (IPCE) measurement, it is clearly demonstrated that only the amorphous phase and Phase II but not Phase I nor Phase Y of TiOPc can contribute to photoelectric conversion in heterojunction photovoltaic cells. This result may come from the low charge generation (exciton dissociation) efficiency of Phase I and Phase Y crystalline structures, which was supported by the change in IPCE curves under inverse bias application. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.091601

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

Pearl-chain-type trees under AC voltage have been observed using a high-speed camera. When AC voltage (60Hz) was applied, a bubble was appeared at a tip of needle electrode in silicone gel. The bubble oscillated with 120Hz. After increasing the applied voltage, a linear tree/tube proceeded ahead a certain distance and stopped. Then the bubble was formed at the tips of the tree/tube. The speed of the part of the bubble was slower than the speed of the linear tube. The branching also occurred. This kind of tree is called pearl-chain-type tree. It was observed that the center of the bubble was located slightly from the tip inward.

DOI： 10.1109/ISEIM.2014.6870783

Web of Science

Scopus

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

researchmap

Language：Japanese  

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We investigated small-molecule-based organic photovoltaic (PV) cells with three different electron-donating material layers, two thiophene/phenylene co-oligomers [alpha,omega-bis(biphenyl-4-yl)terthiophene (BP3T) and alpha,omega-diphenyl sexithiophene (P6T)] and copper phthalocyanine (CuPc), and one electron-accepting material layer (C-60). A cascade-type energy relay between the three donor layers occurred, and the incident photon-current conversion efficiency improved in the blue light region, where CuPc has very low optical absorption. An increase in P6T photoluminescence intensity in a two-layer sample (BP3T/P6T) on quartz confirmed interlayer excitation transfer (ET) from BP3T and P6T. The bulk hetero-junction architecture in our interlayer-ET-based organic PV cell was effective. Moreover, P6T appeared to have a relatively long exciton diffusion length of several tens of nanometers. (c) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2012.12.029

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In this study, several naphthalene tetracarboxylic acid diimide (NTCDI) derivatives substituted at the N and N' positions with long normal alkyl chains of different lengths were evaluated as soluble n-type organic thin-film transistor (TFT) materials. NTCDI derivatives with diundecyl (NTCDI-C11), didodecyl (NTCDI-C12), and ditridecyl (NTCDI-C13) exhibited acceptable solubility in chloroform, and their TFTs showed typical n-type TFT performance with relatively high field effect electron mobility (similar to 0.2 cm(2)/V s) after annealing at a workable temperature of 150 degrees C. Although NTCDI with dioctyl (NTCDI-C8) showed good solubility in chloroform, the TFT performance of this material was highly inferior to that of NTCDI-C11, NTCDI-C12, or NTCDI-C13. We could not anneal NTCDI-C8 thin films at workable temperatures in vacuo because of sublimation of the material from the substrates. In contrast, NTCDI with dipentadecyl (NTCDI-C15) and dioctadecyl (NTCDI-C18) exhibited both poor solubility for chloroform and poor TFT performance. In short, these compounds are not suitable as soluble n-type organic TFT materials. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2012.10.038

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We demonstrated that N,N'-diphenylperylene tetracarbonic diimide (PTCDI-Ph) could work as an n-type sensitizing layer for the C-60 n-type layer owing to interlayer excitation transfer (ET) when the PTCDI-Ph layer was placed between the C-60 layer and the aluminum anode coupled with the bathocuproine layer. Well-aligned lowest unoccupied molecular orbitals between C-60 and PTCDI-Ph (-4.55 eV for PTCDI-Ph and -4.5 eV for C-60) and a larger bandgap for PTCDI-Ph than C-60 (2.04 eV for PTCDI-Ph and 2.0 eV for C-60) enabled this interlayer ET-based sensitization. Further, the optical interference effect could be also involved in the sensitization. It was also demonstrated that the combination of both n-type materials C-60 and PTCDI-Ph could successfully reduce the amount of the expensive C-60 used, and a thin C-60 layer was indispensable for efficient charge separation. PTCDI-Ph could work as a light-harvesting n-type material incorporating C-60-based cells to compensate for C-60's weak optical absorption. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2012.12.004

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Here we propose and demonstrate a new approach to wet-processed organic thin-film transistors utilizing highly-stable colloids of small molecular organic semiconductors prepared by laser ablation technique. Highly stable N,N′-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) colloids of 0.1 wt% concentration were prepared successfully by laser ablation technique in acetonitrile. Mean particle size of the prepared PTCDI-C13 colloid measured by dynamic light scattering method was smaller than 50 nm which is also confirmed by a transmission electron microscope observation. By simple drop-casting of prepared PTCDI-C13 colloids, typical n-type OTFTs with good saturation properties were fabricated successfully. The highest electron mobility was 1.1 × 10-3 cm2/Vs and increased up to 0.027 cm2/Vs by post-annealing treatment. © 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2012.10.024

Scopus

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

In order to diagnose the effectiveness of electrical insulation, it is necessary to obtain information regarding the electric field distribution in insulating materials. We have investigated the measurement of electric field vector distributions in liquid dielectrics using an original method. Electric field distributions could be measured in time intervals of milli-seconds by an optical system. In this study, the electric field in a liquid containing space charges was measured, and the change in the electric field caused by the charges in the liquid was examined. Moreover, the space charge distribution in the liquid was also studied. We believe that our study can aid a better understanding of the movement of charges in liquid dielectrics. © 2013 Penerbit UTM Press. All rights reserved.

DOI： 10.11113/jt.v64.2094

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

The tree growth has been usually classified to three stages
inception, propagation and runaway stage under AV voltage. When the two-dimensional (2-D) specimen of silicone rubber was used, the propagation stage was divided to two stages: straight and isotropic growth stages. 2-D specimen is useful to observe AC trees with many branches since the number of the branches of AC tree is usually larger than DC and impulse tree. When the silicone rubber is fabricated, two types of silicone gel is mixed up
one includes catalytic agent. If the mixed ratio is changed from 1:1, silicone rubber has fluidity or viscosity. In theses cases, breakdown or partial discharge phenomena also change. Under certain conditions of gel, tree has been developing with bubble-like and string-like pattern alternatively. This tree is called pearl-chain-like tree. At first the tree developed like bubble and then a projection like cone was generated on the surface of the bubble. The tip of the cone expanded and formed a new bubble. This process was repeated. If two tips of the cone are formed on the surface of the bubble, the branching occurs. The shape of tree is like pearl-chain. The pattern of the tree is usually string (or straight) channel and branching. However In the pearl-chain like tree, string channel has consisted of two channels
bubble and string. Branching has occurred at bubbles. These data is important to investigate the mechanism of tree. © 2013 Penerbit UTM Press. All rights reserved.

DOI： 10.11113/jt.v64.2102

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

The authors report a novel perylene derivative [N,N'-bis(3-dodecyloxy-propyl)- perylene tetracarboxylic diimide, PTCDI-C3OC12] as a soluble high-performance n-type organic semiconductor. The solubility of the PTCDI derivative was increased sufficiently to be handled using wet processes by inserting ether groups in side alkyl chains of the PTCDI derivative. The highest electron mobility obtained for a spin-coated PTCDI-C3OC12 film was 0.52 cm(2)/(V.s) with a very low threshold voltage of ca. 2 V. This high performance of PTCDI-C3OC12 is explained by the large grain size with an appropriate molecular packing pattern and tight intergrain connections. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/APEX.5.041602

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We demonstrated an organic near-infrared (NIR) photodiode on the basis of the bulk heterojunction (BHJ) structure by using tin phthalocyanine (SnPc) and C-60 fullerene with a high incident photon-electron conversion efficiency (IPCE) of 50% at a wavelength of 750 nm. The cell showed optical responses to about 1000 nm and had a specific detectivity D* of 1.59 x 10(11) cm Hz(1/2)/W. The SnPc:C-60 ratio in the BHJ layer influenced the optical response. Higher ratios enhanced NIR sensitivity but reduced the peak IPCE; the optimal ratio was 3 : 1. The optical interference of directly incident light and light reflected from an Al electrode was also examined to enhance the IPCE at longer wavelengths. With a 90-nm-thick C-60 layer, the first antinode of the standing wave at a wavelength of 750 nm was located at the BHJ layer; this layer enhanced the IPCE at 700 and 800 nm but reduced it at 400 nm. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.034103

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

New electron-transporting materials for organic light-emitting devices (OLEDs) based on trisubstituted benzene with both bipyridine and terpyridine, 1,3-bisbipyridyl-5-terpyridylbenzene (BBTB) and 1-bipyridyl-3,5-bisterpyridylbenzene (BTBB), were developed. Glass transition temperatures of BBTB and BTBB were 93 degrees C and 108 degrees C, respectively, and BTBB was completely amorphous with no melting point. Electron mobilities of BTBB exceeded the order of 10(-4) cm(2) V-1 s(-1), while those of BBTB were very high and reached 10(-3) cm(2) V-1 s(-1) at an electric field of approximately 500 kV cm(-2). These high mobilities contributed to a low voltage operation. For example, in the case of the conventional aluminum trisquinolinol (Alq)-based fluorescent OLED with BTBB, current densities of 3.5 mA cm(-2) and 100 mA cm(-2) were reached at voltages of 3.0 V and 4.5 V, respectively. In addition, ionization potentials of BBTB (6.33 eV) and BTBB (6.50 eV) were sufficiently large to confine holes in common emissive layers.

DOI： 10.1039/c2jm16274a

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We investigate the effects of volatile additives in solutions used to prepare thin-film transistors (TFTs) of regioregular poly(3-hexylthiophene) (P3HT). We use the additives trifluoromethylbenzene (TFMB) and methylcyclohexane (MCH) because they are poor solvents for P3HT. The additives improve the performance of the resulting TFTs when the boiling point (T-b) of the major solvent, carbon tetrachloride, is lower than that of the additive. The maximum mobility is (4.0 +/- 60.9) x 10(-2) cm(2)V(-1)s(-1), which is 6.1 times larger than that of TFTs prepared without TFMB or MCH added to the solution; the on/off ratio and the subthreshold slope were also improved. The relative T-b of the solvent and the additive affected the film formation with the amount of TFMB or MCH remaining at the final stage of thin film deposition influencing the precipitation of P3HT aggregates. (C) 2011 American Institute of Physics. [doi:10.1063/1.3553878]

DOI： 10.1063/1.3553878

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

We developed new electron-transporting materials (ETMs) for organic light-emitting devices (OLEDs) based on benzo[1,2,3] triazole and two bipyridines. Four derivatives based on the same skeleton were synthesized with four different substituents: phenyl (BpyBTAZ-Ph), biphenyl (-BP), m-terphenyl (-mTP), and o-terphenyl (-oTP). These BpyBTAZ compounds have good thermal stabilities, and their decomposition temperatures were greater than 410 degrees C, which is significantly higher than that of tris(8-quinolinolato) aluminium (Alq), the conventional OLED material. BpyBTAZ compounds show preferable amorphous nature, and moreover, the glass transition temperatures (T(g)s) of both BpyBTAZ-TP compounds exceed 100 degrees C. Furthermore, BpyBTAZ-BP exhibits no melting point and is fully amorphous. The electron affinities of the materials are as large as 3.3 eV and their electron mobility is sufficiently high. These characteristics accounted for a reduction in the operational voltage of OLEDs with BpyBTAZ compounds compared with the reference device with Alq as an ETM. Specifically, the electron mobility of all the BpyBTAZ compounds exceeds 1 x 10(-4) cm(2) V(-1) s(-1) at an electric field of 1 MV cm(-1). In addition, it was revealed that both BpyBTAZ-TP-based devices showed longer luminous lifetimes and smaller voltage increases during continuous operation at 50 mA cm(-2), compared with the Alq reference device.

DOI： 10.1039/c1jm10901d

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

The authors report that thermal treatment effect on various N,N'-dialkyl-3,4,9,10-perylene tetracarbxylic diimides [PTCDI-Cn, alkyl-dodecyl (n = 12), butadecyl (n = 14), octadecyl (n = 18)] thin-film transistors (TFTs) depends on the substituted alkyl chain length. It is clearly demonstrated that there are two kinds of molecular movements during the thermal treatment on PTCDI films; molecular rearrangement in the same layer and molecular migration from the lower layer to the upper layer. The former is directly related to the grain growth and can be controllable by applying an external electric field. The latter is also related not only to the grain growth but also to the formation of cracks between grains. These two movements show opposite dependence on the alkyl chain length during the thermal treatment; the former is more active in longer alkyl chain, but the latter in shorter one. However, they also have opposite effect to TFT performance, and PTCDI films with longer alkyl chains have great advantage on TFT performance for the thermal treatment. Consequently, PTCDI-C18 TFTs show the highest electron mobility as large as 1.2 cm(2)/V s after the thermal treatment at 140 degrees C. (C) 2010 American Institute of Physics. [doi:10.1063/1.3525997]

DOI： 10.1063/1.3525997

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The authors report magnetic field (MF) induced grain growth of perylene polycrystalline films during vacuum deposition. It is clearly demonstrated that the grain size of perylene polycrystalline film was increased by 2.6 times with a 3.8 kG perpendicular MF to the substrate at the deposition temperature of 30 degrees C. In contrast, the grain size was decreased by applying a parallel MF to the substrate. This MF effect on the grain growth becomes stronger at higher deposition temperature. The mechanism of this MF effect is discussed through the diamagnetic property and the intralayer interaction of the perylene molecules during the nucleation process. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2010.08.005

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We demonstrated the performance of thin-film transistors (TFTs) and single-crystal field-effect transistors (FETs) based on a trifluoromethyl-substituted alternating (thiophene/phenylene)-co-oligomer (AC5-CF3), 1,4-bis(5'-(4 ''-trifluoromethylphenyl)thiophene-2'-yl) benzene. An FET with a fine AC5-CF3 single-crystal demonstrated field-effect mobility as high as 3.1 cm(2) V(-1) s(-1). This value implies that AC5-CF3 must be a useful n-type organic semiconducting material. The performance of AC5-CF3 TFTs depended on the substrate temperatures at which AC5-CF3 thin films were deposited. From the viewpoint of mobility, threshold voltage and sub-threshold slope, we obtained the highest performance at the substrate temperature of 100 degrees C. This was because a higher substrate temperature for deposition enlarged the size of grains in AC-CF3 thin films and improved the characteristics of grain boundaries. However, 120 degrees C depositions of AC5-CF3 induced deep valley-like cracks in the thin films, probably because of the difference between the coefficients of thermal expansion for AC5-CF3 thin films and silicon wafer substrates, resulting in effects such as worsening mobility. AC5-CF3 TFTs prepared at 100 degrees C deposition showed no channel length dependence of the field-effect mobility, and their average field-effect mobility was 0.55 +/- 0.05 cm(2) V(-1) s(-1). (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2010.06.010

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

We demonstrated a highly sensitive red-light photodetector based on a mixed copper phthalocyanine (CuPc) and fullerene C-60 photoactive layer, similar to a so-called bulk heterojunction structure usually used in the field of organic photovoltaics. We incorporated an additional set of organic layers that was composed of two organic p-type semiconductors to reduce the blue-light sensitivities of CuPc- and C-60-based organic photodetectors. We used alpha, omega-diphenyl sexi-thiophene (P6T) and alpha, omega-bis(biphenyl-4-yl)ter-thiophene (BP3T), which are thiophene-based materials and usually have good hole-transporting properties. A thick (>100 nm) P6T layer absorbed blue light, preventing it from reaching the photoactive layer, and a thin (similar to 20 nm) BP3T layer whose band gap was larger than that of P6T blocked excitation energy transfer from P6T to CuPc. Thus, we successfully demonstrated a red-light photodetector with high peak sensitivity and whose current-voltage characteristics did not worsen. The optimal device showed a peak incident photon-current conversion efficiency of 51.7% at 620 nm and a specific detectivity of 4.0 X 10(11) cm Hz(1/2)/W. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3466766]

DOI： 10.1063/1.3466766

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Here we report a highly efficient sublimation purification system using baffles with orifices in the sublimation tube. It is clearly demonstrated that the purity of materials is increased largely by introducing some pieces of baffles with orifices in the high-temperature region (sublimation region), which was confirmed by comparing the melting point (T(m)) and the high-performance liquid chromatography (HPLC) purity with those of purified one by a conventional system. The driving voltages of electroluminescence (EL) devices were also compared and showed the same tendency with the T(m) and HPLC purity data. Not only the purity but also the effective yield of purified materials was also increased by introducing baffles in low-temperature region. Some expected mechanisms of improving the purification efficiency by introducing baffles were also discussed. (C) 2010 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.orgel.2010.01.021

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We incorporated an additional p-type organic semiconductor layer (APL) between the anode and the phthalocyanine layer, which is an indispensable p-type semiconductor layer (IPL) in forming a p/n junction with a fullerene C(60) layer. We used two thiophene/phenylene co-oligomers as the APL. The incorporation increases the short-circuit current density (J(SC)) and enhances incident photon-current conversion efficiency (IPCE) over the wavelength region where the APL shows strong absorption. Combined dependence of the APL/IPL implies that Forster resonance excitation transfer is the main factor in J(SC) and IPCE enhancements. We demonstrate clearly that the 'positive' hole injection barrier at the interface between the APL and the IPL impacts the smooth transportation of holes to the indium-tin-oxide anode. However, the small positive hole barrier of 0.1 eV has no noticeable influence on the fill factor of the current density versus voltage characteristic under photoirradiation, or on those devices with 'negative' hole barriers. (C) 2009 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.orgel.2009.12.023

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The authors report a new concept of sublimation purification system for the purification of organic semiconducting materials; using arrays of partitions for the efficient separation of the target material from impurities. The authors clearly demonstrate that the new system improves the purity of an electron transporting material for organic light-emitting devices (OLEDs), which was confirmed not only by measuring the purity directly but also by evaluating the performance of OLEDs with the material. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.orgel.2008.03.010

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We have prepared nanoparticles of five organic dye molecules by laser ablation of their microcrystals in poor solvents using the third harmonics of nanosecond Nd3+:YAG laser as an excitation light source. Their colloidal solutions were stable for longer than I week without any surfactants. The mean size was almost common to all the dyes (about 50 nm) and its distribution was narrow, which was confirmed by SEM observation. By applying electrophoretic deposition, the homogeneous thin film of quinacridone nanoparticles was fabricated on an indium-tin-oxide electrode. It was demonstrated that the films with different grain size and crystalline phase can be fabricated arbitrarily by using different nanoparticles. Laser ablation is also useful for crystallization of organic molecules, which was demonstrated for a representative organic nonlinear optical material.

DOI： 10.1117/12.771175

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We have prepared quinacridone (QA) colloids with various particle sizes (25-120 nm) and different crystalline phases by nanosecond laser ablation of its microcrystalline powder dispersed in water and fabricated the prepared colloidal particles into homogeneous films on an indium-tin-oxide electrode by an electrophoretic deposition (EPD) method. The nanoparticle-assembled films consist of closely packed nanoparticles and many nanosized pores. We evaluated the porous nature of the film by scanning electron microscopy observation and by measuring the film thickness dependence of the absorption. It was found that the film morphology is sensitive to the applied bias, and the optimum bias for the QA colloid was determined to be about 10 V/cm. We also demonstrated that organic thin films with different grain sizes and crystalline phases can be fabricated arbitrarily by combining the EPD method with nanoparticle preparation by laser ablation.

DOI： 10.1021/jp074300f

Web of Science

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC APPLIED PHYSICS  

We prepared quinacridone (QA) nanoparticles with a mean size of 70 run by nanosecond laser ablation of their microcrystalline powder dispersed in water, and assembled the nanoparticle colloid into a thin film on an electrode by electrophoretic deposition (EPD). The EPD film consists of closely packed QA nanoparticles and shows a photoconductive response similar to the conventional organic films by vacuum deposition. The present fabrication technique is expected to be applied to the preparation of organic nanostructure using nanoparticles as building block for novel electronic and optoelectronic device application.

DOI： 10.1143/JJAP.46.L733

Web of Science

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)  

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

We have investigated metal oxide semiconductor (MOS) characteristics with Ir gate on ZrO2 dielectrics gate structure. The ZrO2 films are grown with atomic layer deposition-method using O-2 and tetrakis (diethyl amino) zircumium (TDEAZ) as a Zr precursor. Some ZrO2 films are also grown with oxygen plasma along with TDEAZ. The ZrO2 grown with oxygen plasma shows the EOT value of 1.39 nm, high k of 18.2 and little hysteresis of 20 mV, whereas EOT and k values of the ZrO2 films grown with O-2 are 1.52 nm, 13.34 nm, respectively. This is due to dense and well-matched stoichiometric ZrO2 and interfacial reaction through the diffusion of oxygen in the oxygen plasma. Metal oxide semiconductor. field effect transistor. (MOSFET),, characteristics of Ir/ZrO2 grown with oxygen plasma/Si gate structured transistor reveals that the effective mobility is 226 cm(2)/Vs at V-GS = 1.5 V, which is slightly smaller than the saturation mobility of 250 cm(2)/Vs. The interface trap density in the ZrO2 grown with oxygen plasma is also lower than that in the ZrO2 grown with O-2.

DOI： 10.1143/JJAP.42.5010

Web of Science

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

Language：Japanese  

researchmap

J-GLOBAL

researchmap

Language：Japanese   Publisher：電気学会  

CiNii Books

researchmap

J-GLOBAL

researchmap

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：English  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese   Presentation type：Oral presentation (invited, special)  

researchmap

Language：English  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Poster presentation  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：English   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Presentation type：Oral presentation (general)  

researchmap