this post was submitted on 05 Dec 2023
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The electrons are all already in the material. They are never created or destroyed just paired and unpaired with holes.
This video might help? from approx 5 minutes. https://www.youtube.com/watch?v=WfP5YdJn-c4
The energy comes from the sun, it excites electrons and holes, causing the cell to hold a small charge, that charge is the potential energy that drives the circuit. It is depleted by electrons flowing back into the P side from the circuit, they cannot go from the N side because of the field across the depletion zone. Recombinant electrons from the circuit can then be excited again, excess electrons in the N side flow out of the silicon into the load so that electrons can move from the load into the P side.
This all happens at once. In a very long time, eventually the very same electron that was originally excited by a photon will recombine in the depletion layer. There isn't any loss here.
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I am getting frustrated because i am pretty sure the qty of electrons is conserved so at some point equilibrium needs to be reached. I read this paper on diffusion lengths and i got confused so i started watching this older lecture about short and open circuit recombinations. My first impression is that the recombination rate (or qty of electrons coming back into the cell) depends on some thickness of material at the very least.
I was definitely wrong about how the whole loops work but that was me being dumb. Again, this is very out of my brain territory. I used to love this stuff though.
I'm not sure I understand the confusion. The material thickness does matter in that thinner materials will resist current flow due to a lack of charge carriers meaning each must travel faster, which means that more charge separation is required for a given recombination rate or current.
If the charge required is too high (more than the potential difference across the depletion zone) then the build up will prevent charge separation after excitation. They will recombine in the depletion zone making a bunch of heat and burning out the cell.
Maybe that's the thing? super thin films under too much irradiation or load cooking themselves due to inability to move excited charges away fast enough?
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short and open circuit recombinations
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