Tetsuji Oda

The University of Tokyo, Tōkyō, Japan

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Publications (140)160.58 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: In plasma medicine, plasma is applied to a wet surface and is often accompanied by dry-gas flow. The dry-gas flow affects water evaporation from the wet surface and influences production of reactive species derived from water vapor, such as OH radicals. In this study, the effect of the dry-gas flow on two-dimensional distributions of humidity and OH radical density are examined by measuring them using laser-induced fluorescence (LIF). First, humidity is measured when nitrogen flows from a quartz tube of 4 mm inner diameter onto distilled water and agar media from 5 mm distance. NO gas is added to the nitrogen as a tracer and humidity is obtained from the quenching rate of NO molecules measured using LIF. This measurement has a spatial resolution of 0.2 mm3 and a temporal resolution of less than 220 ns. The two-dimensional humidity distribution shows that the dry-gas flow pushes away water vapor evaporating from the wet surface. As a result, a low-humidity region is formed near the quartz tube nozzle and a high-humidity region is formed near the wet surface. The thickness of the low-humidity region reduces with increasing gas flow rate. It is 0.1–0.5 mm for the flow rate of higher than 0.3 l min−1. Next, the OH density is measured when a nanosecond pulsed streamer discharge is applied to a distilled water surface with dry-air flow. The OH density decreases with increasing gas flow rate due to decreased humidity. When the flow rate is lower than 0.1 l min−1, the OH distribution is approximately uniform in the plasma region, while the humidity distribution shows a large gradient. The importance of the thin high-humidity region on the flux of reactive species onto the wet surface is discussed.
    Plasma Sources Science and Technology 02/2015; 24(1). DOI:10.1088/0963-0252/24/1/015002 · 3.06 Impact Factor
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    ABSTRACT: The electrical and particle collection characteristics of a 1,200-m3/hr-dry electrostatic precipitator (ESP) and a 400-m3/hr-wet ESP for a 0.7 MW-Oxy-PC (oxygen-pulverized coal) combustion and carbon capture and storage (CCS) pilot plant were evaluated under varying air and oxygen combustion operational parameters of the ESPs. The corona current of a dry ESP reduced by oxy-firing was compared with that for the same applied voltage with air firing, which resulted in a decreased collection performance during oxy-firing at the same applied voltage. However, the decreased collection performance could be avoided by simply increasing the applied voltage to reach the same corona power consumption as with air firing because the collection performance of the ESP was an exponential function of the power consumption divided by the gas flow rate regardless of combustion conditions. The wet ESP used here had a thin water film on the collection plates due to the patented design of the collection plates, with water supplied by gravitational force from holes on the collection plates with TiO2nanoparticles coated on ball blasted surface. The system only consumed water at a rate of 1.7 L/min/m2. The collection efficiency of the wet ESP was higher than 90% even for fine particles and mists, which enabled an overall particle collection efficiency of 99.98% to be achieved with both the dry and wet ESPs, corresponding to total gravimetric emission of 1.8 mg/m3 at the inlet of the CCS facility. The wet ESP had the additional effect of removing SO2 and SO3 at 64.5% and 23.1% efficiency, respectively.
    Journal of Aerosol Science 11/2014; DOI:10.1016/j.jaerosci.2014.07.003 · 2.71 Impact Factor
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    ABSTRACT: An ultraviolet (UV) process using a low-pressure mercury lamp is affected by ambient humidity. It is due to strong influence of humidity on the production of ozone and other radicals by the UV light. In this paper, a photochemical reaction model under the irradiation of a low-pressure mercury lamp is developed, and the effect of humidity on the production of ozone and other radicals [O, O(D1), O2(a1Δg), O2(b1Σg+), OH, HO2, H, and H2O2] by a low-pressure mercury lamp is discussed using the reaction model. The validity of the reaction model is confirmed by comparing the ozone densities calculated using the model with experimentally measured ozone densities, and they showed good agreement. The reaction model shows that the ozone density decreases with increasing humidity for three reasons: (i) attenuation of 185 nm light due to absorption by H2O, leading to a decreased O atom production by O2 + hν(185 nm) ⟶ O + O which is required to produce ozone by O + O2 + M ⟶ O3 + M; (ii) ozone destruction by O3+hν(254nm)⟶O(D1)+O2(a1Δg), where the resulting O(D1) partly reacts with H2O before converting back to O3 after quenching to O; and (iii) an ozone destruction cycle OH + O3 ⟶ HO2 + O2 and HO2 + O3 ⟶ OH + 2O2. The effect of humidity on the densities of other radicals is also discussed using the reaction model.
    Journal of Photochemistry and Photobiology A Chemistry 01/2014; 274:13–19. DOI:10.1016/j.jphotochem.2013.09.012 · 2.29 Impact Factor
  • Yusuke Nakagawa, Ryo Ono, Tetsuji Oda
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    ABSTRACT: Plasma application for environment improvement is desirable. In order to improve the efficiency of toxic gas decomposition by plasma, it is worthwhile to clarify the behavior of radicals in nonthermal plasma. Although previous studies have revealed the behavior of radical densities and temperatures in atmospheric discharge, they are not yet connected to apprehension or simulation of practical toxic gas decomposition by atmospheric plasma. In this study, the coaxial dielectric barrier discharge cylinder reactor is prepared, where the radical behavior and the toxic gas decomposition efficiency can be measured altogether. The density of OH radical is directly measured by laser-induced fluorescence, and trichloroethylene (TCE) decomposition efficiency is also investigated in the same reactor. TCE decomposition efficiency is suppressed as background humidity increases. On another front, OH density measurement in ac barrier discharge indicates that OH density is about 2–4 $times 10^{11} hbox{cm}^{-3}$ in time and spatial average and saturated with increasing humidity. From the saturation pattern, the initial OH density is estimated to be about the order of $10^{14} hbox{cm}^{-3}$ in streamer site. In addition, TCE addition in background reduces OH density, which indicates that OH reacts with TCE. The reason for the suppression of decomposition efficiency with increasing humidity is estimated as a consequence of O radical reduction by water-originated particles.
    IEEE Transactions on Industry Applications 01/2014; 50(1):39-44. DOI:10.1109/TIA.2013.2266891 · 2.05 Impact Factor
  • Atsushi Komuro, Ryo Ono, Tetsuji Oda
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    ABSTRACT: The effect of pulse rise rate on a streamer discharge is investigated through both experiments and simulations. Pulsed voltages with a pulse rise rate of 0.11–0.52 kV ns−1 are applied to point-to-plane electrode configurations, and the effects are observed from ICCD photographs. The streamer emission of light is simulated by a previously developed two-dimensional streamer simulation model, and the simulation results are compared with experimental results. The results show that as the pulse rise rate is decreased, there is a decrease in the discharge current, velocity of the primary streamer, diameter of the streamer channel and emission length of the secondary streamer. The simulated reduced electric field of the primary streamer head remains constant and does not depend on the pulse rise rate. The simulated temporal variations of O and OH radical production show that almost the same number of the radicals are produced in the primary streamer, regardless of the pulse rise rate. However, the radical production in the secondary streamer decreases as the pulse rise rate decreases. Therefore, the pulse rise rate affects the ratio of radical production in the primary streamer to that in the secondary streamer.
    Plasma Sources Science and Technology 06/2013; 22(4):045002. DOI:10.1088/0963-0252/22/4/045002 · 3.06 Impact Factor
  • Shungo Zen, Daiki Saito, Ryo Ono, Tetsuji Oda
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    ABSTRACT: Dye-sensitized solar cells (DSSCs) require the sintering of TiO2 paste at 450–550 °C in their manufacture. However, high-temperature sintering is disadvantageous because it limits the use of materials that cannot withstand high temperatures. We have developed a new technique for reducing the sintering temperature through ultraviolet (UV) treatment of the TiO2 photoelectrode. The UV treatment enables the sintering temperature to be reduced 250 °C while maintaining the energy conversion efficiency.
    Chemistry Letters 06/2013; 42(6):624-626. DOI:10.1246/cl.130147 · 1.30 Impact Factor
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    ABSTRACT: An electrostatic diesel particulate matter filtration system (EDPS) has been tested using 3000 cc diesel engines operating at steady state and standard (European Stationary Cycle (ESC) 13 mode) conditions. The system consisted of a flowthrough filter (FTF) and a charging device with a round perforated plate imposing an electrostatic field onto the FTF. An insulating device for the high-voltage electrode was protected from pollutant deposition by using an air slit at velocity of 7 m/s to maintain a stable corona discharge under an exhaust temperature exceeding 300°C. Under steady-state engine conditions, the performance test of the EDPS showed high collection performance (based on the particulate matter (PM) number) of nearly 80–99%, while the efficiency of the FTF remained at 15–50%. Comparing the performance of the EDPS with a commercialised diesel particulate filter (DPF) and an FTF under the ESC 13 mode, the EDPS was almost 40% more efficient than the FTF and 10% less efficient than the DPF, while achieving 73% lower pressure drop than the DPF. Thus, the novel filtration system can achieve collection performance similar to the DPF with significantly less pressure drop.
    International Journal of Automotive Technology 06/2013; 14(3). DOI:10.1007/s12239-013-0053-8 · 0.82 Impact Factor
  • Atsushi Komuro, Ryo Ono, Tetsuji Oda
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    ABSTRACT: The production process of OH radicals in an atmospheric-pressure streamer discharge is studied. A streamer discharge model is developed to analyse the characteristics of a pulsed positive streamer discharge in point-to-plane electrodes filled with humid air at atmospheric pressure. The results indicate that the behaviour of OH radicals in and after the discharge pulse is characterized by three reaction processes: 'OH-production', 'OH-cycle' and 'OH-recombination'. The first process of OH-production includes dissociation reactions of H2O with O(1D) and N2, which are the main production processes of OH in the discharge. Immediately after the OH-production process, the OH radicals are destroyed by a reaction with O(3P) to form O2 and H. Then the subsequent reactions produce OH again through the reaction of H + HO2, which is the OH-cycle process. Finally, the OH radicals are consumed by the OH-recombination process.
    Journal of Physics D Applied Physics 04/2013; 46(17):175206. DOI:10.1088/0022-3727/46/17/175206 · 2.52 Impact Factor
  • T. Oda, Y. Nakagawa, R. Ono
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    ABSTRACT: Optical diagnosis of high pressure plasma is one of the most powerful tools for investigating chemical reaction mechanisms in the high pressure plasma region. The authors developed various optical measurement systems by using tunable lasers, such as (two-photon-)laser-induced-fluorescence, coherent-anti-Stokes Raman scattering, time evolution of optical emission imaging and others for detecting O3, O, OH, N, NO* and other radicals in atmospheric pressure plasma. Outline of basic measuring techniques developed by the authors for high pressure plasma diagnosis are explained and real examples of plasma diagnosis are demonstrated in this paper. For example, density distributions of single nitrogen (N) and excited nitrogen molecule (N2(A)) below the discharge needle generated by the pulse plasma suggest that single N might be generated in the secondary streamer, while N2(A) might be generated in the primary streamer, and single N decomposes NO more than N2(A).
    Journal of Physics Conference Series 03/2013; 418(1):2101-. DOI:10.1088/1742-6596/418/1/012101
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    ABSTRACT: A novel positive-polarity electrostatic precipitator (ESP) was developed using an ionization stage (0.4 x 0.4 x 0.14 m(3) ) with 16 carbon fiber ionizers in each channel and a collection stage (0.4 x 0.4 x 0.21 m(3) ) with parallel metallic plates. The single-pass collection efficiency and clean air delivery rate (CADR) were measured by standard tests using KCl particles in 0.25-0.35 μm. Performance was determined using the Deutsch equation and established diffusion and field-charging theories, and also compared with the commercialized HEPA filter type air cleaner. Experimental results showed that the single-pass collection efficiency of the ESP ranged from 50 to 95% and decreased with the flow rate (10 to 20 m(3) /min) but increased with the voltage applied to the ionizers (6 to 8 kV) and collection plates (-5 to -7 kV). The ESP with 18 m(3) /min achieved a CADR of 12.1 m(3) /min with a voltage of 8 kV applied to the ionization stage, and with a voltage of -6 kV applied to the collection stage. The concentration of ozone in the test chamber (30.4 m(3) ), a maximum value of 5.4 ppb over 12 hours of continuous operation, was much lower than the current indoor regulation (50 ppb). © 2013 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd.
    Indoor Air 02/2013; 23(5). DOI:10.1111/ina.12037 · 4.20 Impact Factor
  • Y. Nakagawa, R. Ono, T. Oda
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    ABSTRACT: In order to solve air pollution problem, atmospheric plasma application is desirable. In this study, we realized the real-time OH density measurement in trichloroethylene (TCE) decomposition by coaxial cylinder pulsed barrier discharge. Laser-induced fluorescence measurement indicated that OH density is about 30 ppm at 3 μs after discharge when +28 kV is applied. As for the negative discharge, OH measurement revealed that OH production is almost the same but OH density is about a half compared to those in positive discharge, due to the difference in streamer radius. The TeE addition in background accelerated OH decay, and by chemical reaction simulation, OH-TeE reaction coefficient was estimated to be about 2.3 × 10-12 [cm3/s]. Humidity effect on TeE decomposition efficiency in N2 pulsed barrier discharge is also investigated using the same reactor. The increasing humidity resulted in enhancement of TeE decomposition efficiency, indicating that OH plays important role in TeE decomposition.
    Industry Applications Society Annual Meeting, 2013 IEEE; 01/2013
  • Atsushi Komuro, Ryo Ono, Tetsuji Oda
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    ABSTRACT: A streamer discharge has been considered to be an effective production source of chemically active radicals. However, theoretical understanding of the discharge phenomenon and the chemical kinetics is still poor. This study is devoted to reveal the radical behaviors in an atmospheric pressure streamer discharge in H2O/O2/N2 gas mixtures. The present model includes a discharge model, a gas dynamics model and chemical kinetics model with vibrationally excited molecules. It is shown that the numerically obtained axial distributions of O, N and OH radical are consistent with our experimental results. Direct dissociation processes, two-step dissociation with vibrationally excited molecules and a quenching of excited O atoms are predominant for O, N and OH radical productions, respectively. In addition, a gas temperature and decay rates of radicals in post-discharge periods are also compared with our experimental results. Numerically simulated gas temperatures in post-discharge phase increase as humidity increase. This tendency has already shown in our previous experimental results and it is successfully reproduced in our model. It is also shown that the rise in gas temperature affects subsequent radical decay processes.
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    ABSTRACT: Dye-sensitized solar cell (DSSC) is receiving increasing attention as low-cost photovoltaic device. The DSSC has a nanoporous TiO 2 electrode made by sintering a TiO 2 paste applied on a conductive glass plate at 450-550 °C. To improve the performance of the TiO 2 electrode, we have developed surface treatment of the TiO 2 electrode using dielectric barrier discharge (DBD). The DBD treatment improves the energy conversion efficiency, η, of DSSC by a factor of 1.1. In addition, the DBD treatment has an effect of lowering the sintering temperature, T s , of TiO 2 paste. Without the DBD treatment, η decreases with T s and becomes 0% for T s ≤ 300 °C. On the other hand, with the DBD treatment, η = 0.8η 0 for T s = 300 °C and η = 0.3η 0 for T s = 150 °C, where η 0 is the energy conversion efficiency for DSSC sintered at 450 °C without the DBD treatment. The DBD treatment is also applied to plastic substrate DSSC in addition to the glass substrate DSSC. However, the DBD treatment causes damage to the TiO 2 electrode and cannot be applied to the plastic substrate DSSC. More moderate DBD treatment is required for the plastic substrate DSSC to avoid the damage on the TiO 2 elec-trode.
  • Seiya Yonemori, Ryo Ono, Tetsuji Oda
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    ABSTRACT: An atmospheric-pressure helium plasma jet is getting much attention because of its low heat load. It is known that active species such as OH radical play important role in many plasma processes, for example, in plasma medical care or in plasma sterilization. When using the plasma jet for surface treatment, it is important that the amount of OH radical provided into objectives. We measured OH density in the vicinity of the surface of objectives using laser induced fluorescence (LIF). The plasma jet was generated when AC 8 kHz, 10 kV was applied. When the plasma jet extended onto the dry glass surface, the maximum OH density was 0.2 ppm. On the other hand, the maximum OH density was 1 ppm when the plasma jet extended onto the wet surface. In addition, time-evolution of OH density between two successive voltage pulses was measured. On the edge of the plasma jet, OH density was at maximum and rapidly decreased between two pulses. Those results suggest that there are three ways of OH production; first, the dissociation of H2O included in discharge gas; secondly, the dissociation of H2O included in the ambient air; finally, the dissociation of H2O evaporates from the wet surface.
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    ABSTRACT: To remove particles in corrosive gases generated by semiconductor industries, we have developed a novel non-metallic, two-stage electrostatic precipitator (ESP). Carbon brush electrodes and grounded carbon fiber-reinforced polymer (CFRP) form the ionization stage, and polyvinyl chloride collection plates are used in the collection stage of the ESP The collection performance of the ESP downstream of a wet scrubber was evaluated with KC1, silica, and mist particles (0.01-10 pm), changing design and operation parameters such as the ESP length, voltage, and flow rate. A long-term and regeneration performance (12-hr) test was conducted at the maximum operation conditions of the scrubber and ESP and the performance was then demonstrated for 1 month with exhaust gases from wet scrubbers at the rooftop of a semiconductor manufacturing plant in Korea. The results showed that the electrical and collection performance of the ESP (16 channels, 400x400 mm2) was maintained with different grounded plate materials (stainless steel and CFRP) and different lengths of the ionization stage. The collection efficiency of the ESP at high air velocity was enhanced with increases in applied voltages and collection plate lengths. The ESP (16 channels with 100 mm length, 400x400 mm2x540 mm with a 10-mm gap) removed more than 90% of silica and mistparticles with 10 and 12 kV applied to the ESPat the air velocity of 2 m/s and liquid-to-gas ratio of 3.6 L/m3. Decreased performance after 13 hours ofcontinuous operation was recovered to the initial performance level by 5 min of water washing. Moreover during the 1-month operation at the demonstration site, the ESP showed average collection efficiencies of 97% based on particle number and 92% based on total particle mass, which were achieved with a much smaller specific corona power of 0.28 W/m3/hr compared with conventional ESPs.
    Journal of the Air & Waste Management Association (1995) 08/2012; 62(8):905-15. DOI:10.1080/10962247.2012.686893 · 1.17 Impact Factor
  • Yutaka Soda, Tetsuji Oda
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    ABSTRACT: The giant-magnetoresistive head suffers magnetic damage from electrostatic discharge (ESD) current on the order of 10 mA and thermal damage from ESD energy on the order of 0.5 nJ. The discharge between 2-pF capacitors at 10 V gave a peak current of 34 mA, and the discharge between 100-pF capacitors at 100 V reached 1.5 A. The peak current arose on the order of picofarads and was approximately maximized at the same value of both capacitors. Theoretical energy loss was estimated by the difference between the potential energies prior to and following the discharges. The energy loss was 0.05 nJ for 2-pF capacitors at 10 V and increased in excess of 0.5 nJ for greater than 20-pF capacitors. Therefore, the discharge between picofarad capacitances tends to cause the magnetic damage, and increasing the capacitance causes the thermal damage. Comparison of the potential energy loss and the current energy derived that the contact resistance varied from more than 200 to few ohms as the voltage and the energy loss increased.
    IEEE Transactions on Industry Applications 07/2012; 48(4):1189-1194. DOI:10.1109/TIA.2012.2199954 · 2.05 Impact Factor
  • Atsushi Komuro, Ryo Ono, Tetsuji Oda
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    ABSTRACT: A streamer discharge model is developed to analyse the characteristics of a pulsed positive streamer discharge in point-to-plane electrodes filled with oxygen–nitrogen mixed gas at room temperature and atmospheric pressure. In this paper we study the mechanisms of O and N radical production in an atmospheric-pressure streamer discharge. To confirm the validity of the simulation model, the discharge emission of light and the discharge current are compared with experimental data at several voltages in gas mixtures with 2–20% oxygen concentrations. The calculated streak picture and the axial distribution of streamer luminous intensity are in good agreement with our previous experimental results. After demonstrating the reliability of the model, we performed a numerical study on radical production by the streamer discharge. The experimentally obtained axial distributions of oxygen radical production in O2(20%)/N2 and nitrogen radical production in O2(2%)/N2 are successfully reproduced in our simulation. For the production of nitrogen radicals, two-step dissociation through the vibrationally excited states is predominant.
    Journal of Physics D Applied Physics 06/2012; 45(26):265201. DOI:10.1088/0022-3727/45/26/265201 · 2.52 Impact Factor
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    ABSTRACT: The absolute density of OH radicals in an atmospheric-pressure helium plasma jet is measured using laser-induced fluorescence (LIF). The plasma jet is generated in room air by applying a pulsed high voltage onto a quartz tube with helium gas flow. The time-averaged OH density is 0.10 ppm near the quartz tube nozzle, decreasing away from the nozzle. OH radicals are produced from water vapour in the helium flow, which is humidified by water adsorbed on the inner surface of the helium line and the quartz tube. When helium is artificially humidified using a water bubbler, the OH density increases with humidity and reaches 2.5 ppm when the water vapour content is 200 ppm. Two-dimensional distribution of air–helium mixture ratio in the plasma jet is also measured using the decay rate of the LIF signal waveform which is determined by the quenching rate of laser-excited OH radicals.
    Journal of Physics D Applied Physics 06/2012; 45(22). DOI:10.1088/0022-3727/45/22/225202 · 2.52 Impact Factor
  • Yoshiyuki Teramoto, Ryo Ono, Tetsuji Oda
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    ABSTRACT: To study the production mechanism of atomic nitrogen, the temporal profile and spatial distribution of atomic nitrogen are measured in atmospheric pressure pulsed positive corona discharge using two-photon absorption laser-induced fluorescence. The absolute atomic nitrogen density in the streamer filaments is estimated from decay rate of atomic nitrogen in N{sub 2} discharge. The results indicate that the absolute atomic nitrogen density is approximately constant against discharge energy. When the discharge voltage is 21.5 kV, production yield of atomic nitrogen produced by an N{sub 2} discharge pulse is estimated to be 2.9 - 9.8 Multiplication-Sign 10{sup 13} atoms and the energy efficiency of atomic nitrogen production is estimated to be about 1.8 - 6.1 Multiplication-Sign 10{sup 16} atoms/J. The energy efficiency of atomic nitrogen production in N{sub 2} discharge is constant against the discharge energy, while that in N{sub 2}/O{sub 2} discharge increases with discharge energy. In the N{sub 2}/O{sub 2} discharge, two-step process of N{sub 2} dissociation plays significant role for atomic nitrogen production.
    Journal of Applied Physics 06/2012; 111(11). DOI:10.1063/1.4722317 · 2.19 Impact Factor
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    ABSTRACT: The manufacture of the dye-sensitized solar cell (DSSC) requires the sintering of TiO2 paste at 450--550 °C. High-temperature sintering is disadvantageous because it prevents the use of the materials with poor resistance to high sintering temperatures (e.g., substrate and transparent electrode). In this study, we develop a new technique of reducing the sintering temperature to 250--300 °C using dielectric barrier discharge (DBD) treatment. The DBD treatment of a 250--300 °C-sintered sample has the effects of removing the organic binder in the TiO2 paste, accelerating the necking of TiO2 nanoparticles, and chemically modifying the TiO2 surface. As a result, the energy conversion efficiency of low-temperature-sintered DSSC becomes approximately equivalent to 450--550 °C-sintered DSSCs. DBD treatment is also applied to a binder-free TiO2 paste that was developed for the low-temperature sintering of plastic substrate DSSCs. The energy conversion efficiency of the binder-free paste DSSC sintered at 150 °C is improved by a factor of 1.4 using DBD treatment.
    Japanese Journal of Applied Physics 05/2012; 51(5):6201-. DOI:10.1143/JJAP.51.056201 · 1.06 Impact Factor

Publication Stats

1k Citations
160.58 Total Impact Points


  • 1990–2015
    • The University of Tokyo
      • • Department of Electrical and Electronics Engineering
      • • Department of Electrical Engineering and Information Systems
      • • Department of Advanced Energy
      • • Department of Medical Engineering
      Tōkyō, Japan
  • 2011–2012
    • Korea Institute of Machinery and Materials
      Sŏul, Seoul, South Korea
  • 2005
    • Kyungnam University
      Changnyeong, South Gyeongsang, South Korea
  • 2004
    • Tokyo Electron
      Edo, Tōkyō, Japan
  • 1998–2001
    • Kumamoto University
      Kumamoto, Kumamoto, Japan