Shungo Zen

Development of Low-Temperature Sintering Technique for Dye-Sensitized Solar Cells Combined with Dielectric Barrier Discharge Treatment

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.

Low temperature (150 °C) fabrication of high-performance TiO2 films for dye-sensitized solar cells using ultraviolet light and plasma treatments of TiO2 paste containing organic binder

Dye-sensitized solar cells (DSSCs) require annealing of TiO2 photoelectrodes at 450 °C to 550 °C. However, such high-temperature annealing is unfavorable because it limits the use of materials that cannot withstand high temperatures, such as plastic substrates. In our previous paper, a low-temperature annealing technique of TiO2 photoelectrodes using ultraviolet light and dielectric barrier discharge treatments was proposed to reduce the annealing temperature from 450 °C to 150 °C for a TiO2 paste containing an organic binder. Here, we measure the electron diffusion length in the TiO2 film, the amount of dye adsorption on the TiO2 film, and the sheet resistance of a glass substrate of samples manufactured with the 150 °C annealing method, and we discuss the effect that the 150 °C annealing method has on those properties of DSSCs.

Low-temperature sintering for plastic dye-sensitized solar cells using conventional TiO2 paste containing organic binders

Dye-sensitized solar cells (DSSCs) require sintering of TiO2 photoelectrodes at 450 °C to 550 °C. However, high-temperature sintering is unfavorable because it limits the use of materials that cannot withstand high temperatures. In previous papers, we proposed a surface treatment of TiO2 photoelectrodes to reduce the sintering temperature from 500 °C to 250 °C using a dielectric barrier discharge and ultraviolet light from a low-pressure mercury lamp. In this study, we improved the surface treatment of TiO2 photoelectrodes to further reduce the sintering temperature from 250 °C to 150 °C using a conventional TiO2 paste that contains organic binders. The sintering temperature of 150 °C is critical because it is the maximum tolerable temperature of plastic substrates. The improved surface treatment is applied to both glass and plastic substrate DSSCs. The energy conversion efficiency of glass and plastic substrate DSSCs sintered at 150 °C using our improved surface treatment are approximately 110% and 80%, ...

Study on molten bridge behaviors with arc-less current commutation in a hybrid DC circuit breaker

Hybrid DC circuit breaker (HDCCB), which combines a mechanical switch and a semiconductor, has become a research focus due to a rapid development of DC power system and its low on-state loss and short break time. However, there is still serious arc erosion for a conventional HDCCB because the current commutation is driven by the arc. A novel topology of HDCCB was proposed in former research. It is established based on a SiC-MOSFET which enables it possible to commutate current just in the molten-bridge stage. Thus an arc-less commutation is achieved. In this paper, firstly the influence of commutation on molten bridge is studied by comparing the molten bridge behaviors with and without current commutation when load is 60 V/150 A. And then, it is investigated how current value, separation speed and contact materials affect molten bridge performances in commutation condition. The experiments are carried out by using Cu and W contacts in open air when current is increased from 50 A to 200 A and the separation speed ranges from 0.04 m/s to 0.16 m/s. The results of this paper are meaningful for the optimization of this arc-less commutation hybrid DCCB.

Development of an arcless DC circuit break using a mechanical contact and a semiconductor device

Direct current circuit breakers (DCCBs) have receive considerable attention due to their increasing demand in DC power transmission and distributed generation. A hybrid DCCB comprising a mechanical contact, semiconductor device (SiC- MOSFET), and metal oxide varistor offers a small contact resistance when the mechanical contact is closed. After opening the mechanical contact, the contact voltage increases because a molten metal -bridge is formed between the contacts as a result of joule heating. This molten-bridge voltage promotes the current commutation from the mechanical contact to the SiC-MOSFET. After the current commutation is completed, a fast current interruption can be achieved by turning off the SiC-MOSFET. Therefore, the hybrid DCCB can achieve both a small contact resistance and a fast current interruption. In our previous papers, an arcless commutation was reported at the initial stage of the hybrid DCCB opening under a special condition. In this report, higher molten-bridge voltage was obtained using 2-pole contacts connected in series and using high-boiling metals. The higher molten-bridge voltage enabled the hybrid DCCB to interrupt larger current without any arc discharge. Finally, we performed DC current (300 V-150 A) interruption experiment, and succeeded in obtaining arcless current interruption with a probability of 100%.

Development of low-temperature sintering technique for plastic dye-sensitized solar cells

Dye-sensitized solar cell (DSSCs) requires sintering of TiO2 photoelectrode at 450~550 °C to be manufactured. However, the high-temperature sintering is disadvantageous because it limits the use of materials that cannot withstand high temperatures. In our previous work, we proposed plasma and low-pressure mercury (Hg) lamp ultraviolet (UV) treatments of the TiO2 electrode to reduce the sintering temperature by half. It was concluded that the effect of the surface treatment is due to reactive oxygen species (O3, O, OH) produced by the plasma and UV light. In this paper, we propose a new technique for TiO2 photoelectrode, which can reduce the sintering temperature from 450°C to 150°C. We were also succeeded in manufacturing plastic DSSC at 150-°C sintered by using the new technique. The conversion efficiency of plastic DSSC was 2.9 %.