how photovoltaic cells work?

elpitu1974

i'm very interested in learning about photovoltaic cells, i've read in some sites already but they all describe it in very general way, can anyone tell me on detail how does it work?
thanks

chill_factor

the simplest solar cell is a p-n junction diode sandwiched between 2 electrodes. a p-n junction is most easily created by a single piece of semiconductor doped with V group elements (electron donors) on one side and III group elements (electron acceptors) on the other. the purpose of the p-n junction is to introduce different charge carriers on either side. note that the piece of silicon after doping is still neutral as we are adding neutral atoms to both sides.

in a p-n junction, electrons near the junction start to diffuse from the n side to the p side due to the difference in chemical potential of electrons. however this creates an electrostatic field near the junction that will end the diffusion. the excess electrons in the conduction band on the n side diffusing away into the p side results in a positive charge on the n side and a negative charge on the p side. the region that shows diffusion is called the depletion layer. the voltage associated with this electrostatic field is called the built in voltage. far away from the junction, of course, the material is unaffected.

a photon with energy greater than the bandgap of the material is absorbed by an electron in the valence band. the electron is promoted to the conduction band and leaves behind a hole that acts as an effective positive charge.

due to the built in voltage the electron migrates towards the N side of the depletion layer. the hole migrates towards the P side of the depletion layer. this serves as the EMF once the circuit is completed and an external load is attached.

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