Crystalline Silicon Solar Cells, Ultrathin Wafer, Multi Wire Sawing, Slicing, Diamond Coated
Summary / Abstract:
Ultra-thin silicon wafers are suitable for needs such as to reduce the weight of solar cells and realize PVpowered vehicles, with great advantages of bendability and lightweight. Multi diamond-wire sawing has become main stream for wafer slicing in Si solar cell industry because of its high productivity. For thin wafers, it is important to realize high precision slicing to prevent breakage. We evaluated the relationship between sawing damage and crystallinity in order to clarify the cause of wafer breakage and establish low damage slice conditions. It is confirmed that the crystallinity differs depending on the slice conditions. There is significant amount of a-Si phase, crystalline defects on the poor-controlled slicing surface, while the well-controlled surface shows almost only single-crystalline Si phase. Furthermore, we found that the well-controlled smooth surface provided the higher tolerance for the breakage. As a result, the highly flexible ultrathin wafer is obtained with well-controlled surface crystallinity. The PERT cell fabrication using ultra-thin wafers showed that the relative deference of cell efficiency between 166 μm and 84 μm-thick solar cells was as small as only 1.2% (relative).