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silicone to prevent solar cell oxidation?

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Posted by Bernhard Kuemel on July 11, 2013, 6:07 pm

In this video

the guy says Sylgard 184, a brand of silicone, protects the cells from
moisture, the environment and oxygen. "You won't get 30 years out of
these if they're exposed to oxygen."

Now I wonder two things.

Firstly, isn't silicone "highly" permeable to gas? Does it really
protect from oxygen?

Secondly, is oxygen really a problem? I guess the semiconductor is
immune, cause oxygen forms a highly stable and protective silicon oxide
passivation layer. But there's also contact fingers and bus bars made of
silver paste and other materials and solder connections.

Is Sylgard 184 silicone really a suitably protective encapsulant? I also
found POLASTOSIL M-2000 which is supposed to be like SYLGARD 184:
http://www.ebay.com/itm/271079655104  . Do you think that's good, too?

Thanks, Bernhard

Posted by bethie on July 11, 2013, 8:17 pm

nice stuff, no byproducts at all

they have been using silicone in many situations, spacecraft electronics,
GE makes some nice stuff,  it is like a soft white plastic when hard no  
bubbles likes hign voltage too, moisture cannot get through

and it is the metal contacts that would corrode

has to keep out moisture as well.  

Posted by Salmon Egg on July 12, 2013, 6:21 pm

Most silicon based semiconductors purposely use silicon oxide for  
protective purposes. There is silicon monoxide with relatively high  
refractive index and silicon dioxide. I am not all that familiar with  
the chemical prooerties as deposited on silicon. I presume it is  
possible to get various compositions between the monoxide and dioxide. I  
doubt that these deposit epitaxially. They may even deposit in amorphous  
layers. In any event, such deposits are likely to provide some  
antireflection for the cells.



Conservatives are against Darwinism but for natural selection.
Liberals are for Darwinism but totally against any selection.

Posted by Mark Thorson on July 13, 2013, 1:07 am
 Bernhard Kuemel wrote:

Yes, it is highly permeable to gases.

Silicones are commonly used as "glob top" encapsulants
for chip-on-board packaging, i.e. where a chip is glued
to a circuit board and then wire-bonded.  Silicone is
extremely hydrophobic, so it keeps the water out.

If it's a platinum-catalyzed addition cure silicone,
that's good.  Other cure systems may produce corrosive
byproducts, such as ammonia.  Some materials can
inhibit the platinum catalyst, so you have to watch out
what materials the silicone will be in contact with.

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