Photovoltaics: Does a Solar Cell Need Current to Work?

[EvaristeG]

Hello everyone !

I have a very basic question about phovoltaics: does a photovoltaic solar cell need to be current to work ? I mean it sounds stupid since we use solar cell to produce current and not the opposite... The fact is I do not really understand how the cell produces current, I was thinking that something like a external voltage is missing to create the current flow..

What I understood is that when you take the n-type silicon and the p-type silicon and put them together to form the pn junction a depletion zone is formed where you don't have any carrier... Due to the inbalance of the charges between the n side and the p side an electric field is formed (around 0.6-0.7 volts for Silicon)...and then ? Electrons from the n side would like to couple with the holes on the p side but they can't because of the depletion zone and therefore if you give them an external "track" they will flow through that circuit and is how current is produced ?

I don't know, I have the feeling I'm missing something..could anyone help me and explain me how it works ? I mean how you really get the current (the user could use) in the end ? Also is you need to supply the cell with power or not, which I know sounds weired but still, I'd like to know... I mean, you need to supply a photodiode don't you ? So what's the difference ?

Thank you very very much in advance for any help !
Evariste

 

[Naty1]

http://en.wikipedia.org/wiki/Photovoltaic_cell

http://en.wikipedia.org/wiki/Photovoltaic_effect

In the case of a p-n junction solar cell, illumination of the material results in the creation of an electric current as excited electrons and the remaining holes are swept in different directions by the built-in electric field of the depletion region.[2]