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Some sources say that when a photon hits the PV cell, it breaks apart electron-hole pairs. Other sources say that photons create electron-hole pairs. Can anyone explain which one is right? I've read several explanations of what goes on in the solar cell, but they don't seem very clear. To me, who has little prior knowledge, a few aspects of the many different explanations seem to contradict each other. I don't know if it's because some of the explanations said things a certain way for simplicity's sake, but this part seems too significant to ignore.

For example, http://www.solarenergyexperts.co.uk/buyersguides/photovoltaic-glass-how-does-it-work/ : "When photons (light particles) from the sun hit the cell, the energy breaks up the paired particles. The freed electrons go into the n-type layer, while the holes go down into the p-type layer."

http://science.howstuffworks.com/environmental/energy/solar-cell3.htm : "When light, in the form of photons, hits our solar cell, its energy breaks apart electron-hole pairs."

http://solarjourneyusa.com/bandgaps.php has a hole section called "Generation of electron-hole pairs"

This one basically seems to be talking about the same thing, but doesn't really mention electron-hole pairs, and the explanation seems more confusing to me, but anyway, http://www2.pv.unsw.edu.au/nsite-files/pdfs/UNSW_Understanding_the_p-n_Junction.pdf: "...broken bonds created by the light act as holes ... and these holes are also free to move throughout the material. Electrons and holes created in this way are physically near each other: for every electron excited by the light there is a corresponding hole generated. These electrons and holes can remain excited only for a short period of time. In a process called recombination, excited electrons stray too close to holes and the two fall back into bonded positions." This one seems to be saying that photons break apart the bonds between the electron and its atom, which creates a free electron and a hole, i.e. another one saying that an electron-hole pair is created.

http://solarcellcentral.com/junction_page.html : "When photons hit the solar cell, free electrons attempt to unite with holes in the p-type layer."

http://www.solarenergy.net/Articles/how-photovoltaic-cells-work.aspx : "When enough photons are absorbed by the negative layer of the photovoltaic cell, electrons are freed from the negative semiconductor material."

So what actually happens when light hits a solar cell?

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2 Answers 2

The short answer is that when an electron in the valance band absorbs energy from a photon to become a conduction band (mobile) electron, both that electron as well as the hole "left behind" in the valence band can participate in an electric current. Thus, it is said, an electron-hole pair is created.

Where there was no mobile charge carrier, there are now two; where there was no electron-hole pair, this is now a pair. Remember, a hole is, in reality, a vacancy in the valance band. When this hole is due a valance electron "jumping" into the conduction band, the hole is part of an electron-hole pair.

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Thanks; Also, does the electric field cause the electron to go to the p-type side or the n-type side? I'm getting a lot of conflicting information on that too. –  Seven May 5 '13 at 22:26
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@Seven, if the electron-hole pair (ehp) is created in or near the depletion region, the electric field there (which "points" from the n-type material to the p-type material) will separate the pair with the electron accelerating towards the n-type material and the hole accelerating towards the p-type material. This constitutes an electric current from the n-type to the p-type material. –  Alfred Centauri May 5 '13 at 22:39

"Other sources say that photons create electron-hole pairs.":

Electrons have mass. Creating them even if possible would need a great deal of energy. So this is not what happens when a photon creates electric current in a substance.

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