What is the meaning of this croped part? Why do they crop it, rather than let it be full square?
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2 Answers
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the monocrystalline cells are thinly sliced off cylindrically-grown single crystals that look like logs. Each wafer thus produced is hence a circular disc. To make the resulting solar cell function properly, its active area must be square so the rounded edges of the wafer get sawn off so the wafers can be packed together as closely as possible during bulk processing. The chamfered corners are left.
answered May 21, 2021 at 17:15
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$\begingroup$ Why do they cut the edges? Why don't they leave the sharp edges be? I really do not understand please explain. Why isn't it square like polycrystalline cells? Do they remain big this way? Would it be smaller if it was cut perfectly square? $\endgroup$ Commented May 21, 2021 at 17:36
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2$\begingroup$ I suspect what niels is implying at is that there is one cell per wafer/slice from a round ingot (not many cells per slice as might be the case for integrated circuits), in which case a single square with rounded corners could use up more of the circular area on an the cross section of a round ingot while still be square enough to tessellate. $\endgroup$– DKNguyenCommented May 21, 2021 at 18:37
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$\begingroup$ @DKNguyen, yes that is the point. $\endgroup$ Commented May 22, 2021 at 0:47
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$\begingroup$ Also sharp square corners of single-crystals are very easily broken and produce chips/particulates, unless bevelled/ground down. For single-crystal material, care must be taken to prevent small chips from causing the crystal wafers to cleave (break). Since the circular wafer is already bevelled to prevent cleaving during fabrication, may as well improve the robustness of the cell by leaving some rounded corners. I suspect there is also some calculation as mentioned above to produce the maximum area. $\endgroup$– DemisCommented 9 hours ago
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This question might be a bit old, but I think it is not too late to share knowledge to the world. You might be a bit confused by the first answer, but here I got some visual illustrations and hopefully clear explanation for you to understand why and how mono crystalline photovoltaic cells often has that rounded or cut corner look.
Mono crystalline cells are cut from a single crystal grown in a cylindrical log shape or "boule", which has a circular cross section. It is easy to think that manufacturers might cut corners for cost cutting or something else but that's not what is happening here. Before sliced into thin wafers, the cylindrical silicon crystal boule is cropped/bricked into square blocks just at the right spot so that the cells could be arranged compact enough to produce maximum possible energy without wasting too much space and also there won't be too much wasted material if cropped into perfect square. (The second reason is just my opinion, of course they could just recycle any unused material). If left uncropped, having circular disc shaped cells in a module not only weird but also wastes too much space for lesser efficiency due to the areas not covered by the photovoltaic cells. I'm sure there might be other reasons I didn't mention but this is what I know so far.
For your curiosity, of course there are actually some, mostly newer generation monocrystalline PV cells that doesn't have rounded corners. They're likely made of wafers from bigger diameter crystal boule cut into smaller cells.
Here's an illustration of the manufacturing process of poly crystalline for reference and how they had that perfect squared cut without any corners cut.
All illustrations thanks to AE-Solar
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$\begingroup$ The illustrations are a great addition! $\endgroup$ Commented Oct 6 at 12:02