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I was recently studying about Staebler-Wronski effect observed in amorphous silicon (a-Si). I realised it was due to imperfections in the lattice structure and breaking of Si-Si bond to Si-H bonds.

So if hydrogen atoms will be less the effect will be minimum. Why do we add hydrogen atoms to a-Si?

Is is just to passivate the unsaturated Si atoms at the edges, or am I missing something?

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    $\begingroup$ You are essentially correct. You need to passionate any unsatisfied bonds. $\endgroup$ – Jon Custer Dec 30 '18 at 17:37
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    $\begingroup$ @JonCuster xD my goodness... $\endgroup$ – Mithoron Dec 30 '18 at 18:28
  • $\begingroup$ @Mithoron - Sigh... stupid auto correct. I sense a (niche) market for a technical spell check dictionary... $\endgroup$ – Jon Custer Dec 30 '18 at 18:29
  • $\begingroup$ @JonCuster Oh no! T'is a thing of beauty :D $\endgroup$ – Mithoron Dec 30 '18 at 18:35
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Well, one either adds it on purpose: In order to reduce the defect volume - by passivating the dangling bonds. Unsaturated silicon atoms in a-Si is a serial killer of charge carriers. But then the issue is the SWE - you have to handle it somehow. Options are few but research is being done. The common way of handling it right now is to be honest about it. This pv cell will lose some efficiency the first months, but then stabilize. Not a good selling point, but that is where it is at.

Or one adds it accidentally / coincidentally by using a deposition technique or raw material that contains hydrogen. ($\ce{SiH4}$ or $\ce{SiH_xCl_{4-x}}$). But you can usually thermocycle these problems away, as long as your substrate can handle it. If you did it, accidentally, on a plastic surface - it is usually referred to as "scrap" and recycled...

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