Toward stabilized 10% efficiency of large-area (>5000 cm) a-Si/a-SiGe tandem solar cells using high-rate deposition

This paper reviews recent progress in large-area a-Si/a-SiGe tandem solar cells at Sanyo. Optimized hydrogen dilution conditions for high-rate deposition of hydrogenated amorphous silicon (a-Si:H) films and thinner i-layer structures have been systematically investigated for improving both the stabilized efficiency and the process throughput. As a result, a high photosensitivity of 10⁶ for a-Si:H films has been maintained up to the deposition rate of 15 Å/s. Furthermore, the world's highest initial conversion efficiency of 11.2% which corresponds to a stabilized efficiency of about 10% has been achieved for a 8252 cm² a-Si/a-SiGe tandem solar cell by combining the optimized hydrogen dilution and other successful technologies.     

Purity-enhanced bulk synthesis of thin single-wall carbon nanotubes using iron-copper catalysts

We report high purity and high yield synthesis of single-wall carbon nanotubes (SWCNTs) of narrow diameter from iron-copper bimetal catalysts. The SWCNTs with diameter of 0.8-1.2 nm are synthesized using the zeolite-supported alcohol chemical vapour deposition method. Single metal and bimetal catalysts are systematically investigated to achieve both the enhancement of SWCNT yield and the suppression of the undesired formation of graphitic impurities. The relative yield and purity of SWCNTs are quantified using optical absorption spectroscopy with an ultracentrifuge-based purification technique. For the single metal catalyst, iron shows the highest catalytic activity compared with the other metals such as cobalt, nickel, molybdenum, copper, and platinum. It has been found that the addition of copper to iron results in the suppression of carbonaceous impurity formation without decreasing the SWCNT yield. The purity-enhanced SWCNT shows fairly low sheet resistance due to the improvement of inter-nanotube contacts. This scalable design of SWCNT synthesis with enhanced purity is therefore a promising tool for shaping future high performance devices.     

Secular variation of BHC in the paper of books

In order to consider the distribution, migration and accumulation of the organochlorine compounds in cities, hexachlorocyclohexane (BHC) levels were measured in the paper of books. BCH was always present in books published between 1927 and 1972; the highest concentration was observed in the books published in 1946 but it was not detected (below 1 ng/g) in the paper of books published in 1973. The secular variation of BHC content in the paper of books is considered as an indicator for the use of BHC in Japan.     

P-dichlorobenzene emission rates from moth repellents and leakage rates from cloth storage cases

Emission rates of p-dichlorobenzene (pDCB) from five kinds of commercially available moth repellents and leakage rates from six kinds of commercially available cloth storage cases were measured. The emission rates from moth repellents immediately after purchase (E(max)), which were obtained as the slope of the total emission amount vs. time elapsed, were 0.0033 to 0.035 g/h at 25 degrees C. Moth repellents from different manufacturers differed greatly in emission rates at 0.0033, 0.0060, and 0.011 g/h, even if the moth repellent pieces were of similar shape and initial weight. This is thought to be because emission rates depended on the diffusion resistance of the repellent packing material used by each manufacturer. Therefore, the manufacturer-specific apparent mass transfer coefficients (K) were calculated for each moth repellent from the measured emission rates and a calculated saturated concentration. The apparent mass transfer coefficient K and the concentration gradient between the in-case (inside a cloth storage case) bulk air and the air at the surface of a moth repellent (pDCB tablet) were used for the calculation of the general emission rates. The leakage rates, defined as the air-exchange rate for a cloth storage case, from six cloth storage cases ranged from 0.41 to 78/h. Despite the large difference (more than 100 times) in the leakage rates of the cloth storage cases, the differences in emission rates of pDCB from these cloth storage cases to the indoor environment were small (<30%). This is because the concentration gradients between the in-case bulk air and the air at the surface of a repellent piece were almost the same among the storage cases. This suggests that pDCB emissions from cloth storage cases into the indoor environment should be reduced by making the storage cases more tightly sealable so that the leakage rate is <0.01/h. The results of adsorption tests of pDCB onto woollen clothes showed that the adsorption of pDCB on the clothes was assumed to be very strong and the transfer between the gas phase and the cloth phase in the cloth storage case was assumed to be small. PRACTICAL IMPLICATIONS: The use of pDCB provides benefits such as moth control and deodorizing, but on the other hand, poses potential risks to human health. There is a risk-benefit tradeoff, i.e. a tradeoff between risks of pDCB to human health and benefit of moth control effects. The pDCB concentration in the cloth storage case and in the indoor air can be estimated by using emission rates and the leakage rates obtained in this study. By comparing the concentration to the deterrent efficiency of pDCB, the risk for the use of pDCB moth repellents can be managed.     

Formation of active sites on Ir/WO3–SiO2 for selective catalytic reduction of NO by CO

Pretreatment conditions for the activation of Ir/WO₃–SiO₂ for the selective catalytic reduction of NO by CO in the presence of excess O₂ were studied. Sequential treatment involving calcination in the presence of O₂ and H₂O followed by reduction and then re-oxidation under mild conditions was found to effectively activate Ir/WO₃–SiO₂. Temperature-programmed desorption during calcination, X-ray diffraction, and temperature-programmed reduction by H₂ revealed that calcination was necessary for oxidative removal of the NH₃ ligands from the iridium precursor, that reduction produced metallic iridium and partially reduced tungsten oxide, and that re-oxidation produced tungsten oxide with low reducibility. Transmission electron microscopy revealed that Ir was supported on finely dispersed tungsten oxide and that the iridium particle size after the sequential activation was 1–1.5 nm.     

Use of benzothiadiazole–triphenylamine amorphous polymer for reproducible performance of polymer–fullerene bulk-heterojunction solar cells

An amorphous polymer, poly(BTD-TPA), which consists of benzothiadiazole and triarylamine units, can be successfully utilized to fabricate bulk heterojunction (BHJ) organic photovoltaics (OPVs), and the OPV performance can be demonstrated to be independent of the casting solvent or thermal annealing temperature. The OPV based on poly(BTD-TPA):PC₇₀BM (1:4) that was fabricated using chloroform (boiling point of 61 °C) and annealed at 60 °C for 10 min exhibited a power conversion efficiency (PCE) of 2.81% under simulated solar irradiation through an air mass of 1.5 at 100 mW cm⁻². On the other hand, the OPV fabricated using o-dichlorobenzene (boiling point of 181 °C) and annealed at 110 °C for 10 min exhibited a PCE of 2.65%. Almost the same PCEs and incident photon to current conversion efficiencies (IPCEs) were obtained in both OPVs. The use of an amorphous film of poly(BTD-TPA) in the fabrication of OPVs offers great advantages over the use of a polycrystalline film of regioregular poly(3-hexylthiophene) (P3HT) in terms of high reproducibility of the OPV performance.     

Thermal stability of back side metallization multilayer for power device application

Metallization multilayers on the back side of a power device were focused in this study. Si wafers coated with high melting point metals were exposed at 300 °C for 300 h to investigate diffusion condition of the metallization layer. We developed and examined the thermal stability of die bonding material (Au paste) including sub–micrometer–sized Au particles. Auger electron spectroscopy was applied to observe the atomic composition of the multilayers in depth direction after the high temperature aging. Surface morphology was observed using optical microscope and scanning electron microscope. While atomic composition on Ti/Au changed drastically after the high temperature aging, other multilayers maintained their metallization composition. However, the surface morphology was slightly changed on Ti/Ru/Au, W/Au, and Ta/Au. Bond strength on the Ti/Pt/Au kept over 40 MPa with unified bonding layer after exposing at 300 °C for 1000 h.     

Continuous grinding kinetics of ethenzamide particles by fluidized-bed jet-milling

Continuous grinding kinetics of Ethenzamide powder, as a model active pharmaceutical ingredient (API) was investigated by fluidized-bed jet-milling. Because the oversize fractions after the classification were well fitted by a modified Rosin-Rammler distribution function, an equation of grade efficiency curve was obtained, which was also characteristic of API. A continuous grinding model was developed on the basis of a batch model by using 1st Kapur function relating grinding rate, the grade efficiency curve, and the overall process flow model consisting of grinding, classification, and mixing zones. The residual ratio obtained was well fitted to the experimental results except for the particle size range smaller than 4 microm and larger than 100 microm. Furthermore, because the volume of the active grinding zone adopted as the fitting parameter was found to be 5 cm3 in all experiments and the value was considered to be appropriate dimensionally, this result supports the reliability of the model.     

Changes in Endogenous Oxytocin Levels and the Effects of Exogenous Oxytocin Administration on Body Weight Changes and Food Intake in Polycystic Ovary Syndrome Model Rats

Polycystic ovary syndrome (PCOS) is frequently seen in females of reproductive age and is associated with metabolic disorders that are exacerbated by obesity. Although body weight reduction programs via diet and lifestyle changes are recommended for modifying reproductive and metabolic phenotypes, the drop-out rate is high. Thus, an efficacious, safe, and continuable treatment method is needed. Recent studies have shown that oxytocin (OT) reduces body weight gain and food intake, and promotes lipolysis in some mammals, including humans (especially obese individuals), without any adverse effects. In the present study, we evaluated the changes in endogenous OT levels, and the effects of acute and chronic OT administration on body weight changes, food intake, and fat mass using novel dihydrotestosterone-induced PCOS model rats. We found that the serum OT level was lower in PCOS model rats than in control rats, whereas the hypothalamic OT mRNA expression level did not differ between them. Acute intraperitoneal administration of OT during the dark phase reduced the body weight gain and food intake in PCOS model rats, but these effects were not observed in control rats. In contrast, chronic administration of OT decreased the food intake in both the PCOS model rats and control rats. These findings indicate that OT may be a candidate medicine that is efficacious, safe, and continuable for treating obese PCOS patients.     

Control system for automatic search and transportation of an object by a mobile robot with obstacle avoidance function

Artificial Life and Robotics - In this paper, using image processing and distance measurement, we develop a control system for automatic grasping and obstacle avoidance by a mobile robot. First,...