Impact of Laser Hole Drilling on the Fracture Strength of Metal Wrap-Through (MWT) Solar Cells

We have measured the fracture strength of multi-crystalline silicon (mc-Si) wafers to investigate the possible effect of laser hole drilling on the breakage rate of metal wrap-through (MWT) solar cells. Groups of solar wafers with 0, 100, and 300 holes (130 mu m diameter) were prepared using a UV Q-switched laser. For each group, half of the wafers were subjected to a wet chemical etch (standard HF-HNO3 texture etch). The breakage force was measured with a plate-twist test apparatus. For the unetched wafers, a strong correlation could be found between the number of laser-drilled holes and the breakage force. For the etched wafers, however, no statistically significant difference could be found between the different groups. Our results indicate that the microcracks created by our UV laser-drilling process can be successfully treated with the standard texture etch, in contrast to the previous studies using IR and green lasers. DOI:10.2961/jlmn.2011.03.0016