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Surface modification technology was applied to hot-dip galvanized steel sheets (HDG) in order to improve their press formability. The frictional behavior and press formability of surface modified HDG were investigated in comparison with those of conventional HDG, conventional electrogalvanized steel sheets (EG) and pre-phosphate treated EG (EG pre-phos). Specimens of these coated mild steel sheets with various mechanical properties were used as test materials. The friction coefficient was measured by a flat sliding test, and press formability was evaluated by a deep drawing test and a stretch forming test. As a result, surface modified HDG showed a lower friction coefficient and higher press formability than conventional HDG and conventional EG. The friction coefficient and press formability of surface modified HDG were similar to those of EG pre-phos. In deep drawing, the inflow of material from the flange area to the cracking area becomes easier due to the lower friction coefficient of surface modified HDG, which leads to improvement of deep drawability. In stretch forming, the outflows of material from the sheet/punch contact area to the cracking area become easier due to the lower friction coefficient of surface modified HDG, leading to improvement of stretch formability. These results indicate that surface modified HDG is a promising material for automotive use.

The effect of aging time after production on the frictional characteristics of hot-dip galvanized steel sheets (HDG) was examined in this study to stabilize and improve the press formability of HDG. Conventional HDG with the Zn coating weight of 67 g/m2 including 0.36 mass% Al were used as test specimens. The specimens were aged for a predetermined period, after which their friction coefficients were measured with a flat sliding test. It was found that an Al-based oxide grew on the HDG surface and the friction coefficient tended to decrease with increased aging time. This suggests that the Al-based oxide reduced the friction coefficient. To understand how the Al-based oxide affects the friction coefficient, surface observation and analysis of both the test specimens and the tools after sliding were carried out. Although the Al-based oxide was not detected on the HDG surface in the area of contact with the sliding tool, the oxide was detected as adhering material on the tool surface after sliding, suggesting that the adhering material on the tool reduced the adhesion force between the metallic Zn of the HDG and the tool. This could lead to a lower friction coefficient because shearing resistance was decreased.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 1102-1105, In order to reduce the power-generating cost of crystalline silicon-based solar cells, it is necessary to achieve a high conversion efficiency with thinner crystalline silicon wafers. The Voc of a very thin HIT solar cell reached 747 mV by improving the passivation capability of the a-Si/c-Si interface. The Hall mobility of a transparent conductive oxide increased 1.3 times. With these technical improvements, the conversion efficiency of the HIT solar cell rose to 23.0%. In order to suppress the production cost, we also applied these improvements to thin HIT solar cells. We successfully obtained a conversion efficiency of 22.8% for a 98-μm-thick HIT solar cell. Because of its excellent conversion efficiency, the HIT solar cell has received much attention, and many researchers have been studying amorphous–silicon/crystalline-silicon heterojunction solar cells.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1690-1693, In order to reduce the power-generating cost of a silicon solar cell, it is necessary to use a thinner crystalline silicon (c-Si) wafer together with the excellent light trapping and well passivated surface that are essential for high-efficiency solar cells. The HIT (Heterojunction with Intrinsic Thin-layer) solar cell is an amorphous silicon (a-Si)/c-Si heterojunction solar cell that has these features. We have experimentally confirmed that the Voc of the HIT solar cell increased with decreases in the cell thickness and can reach more than 0.74 V. This indicates that the surface recombination velocity of the HIT structure is extremely low due to excellent passivation on the c-Si surface. A conversion efficiency of 22.8 % has been achieved with a 98-μm thick CZ c-Si (100.3-cm2) cell.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1136-1139, For reducing the power-generating costs, the following approaches are discussed; (i) enhancing the conversion efficiency, (ii) utilizing a thin wafer for the HIT cell, (iii) improving the temperature coefficient, and (iv) applying HIT solar cells to bifacial solar modules. Furthermore, we have exhibited a high potential for use on thinner c-Si wafers. The high conversion efficiency of 21.4% and an extremely high Voc of 0.739 V were obtained with 85-μm- thick HIT cell. The benefits of using HIT solar cells for bifacial solar modules are also described.