Undergrad Trying to understand the inner workings of a solar cell

[Jman99]

I understand the basics but one thing sticks out in my mind which I cant make sense of, on the N side there are alot of electrons just sitting there like a gas (presumably with 0 net charge) held back by the internal electric field at the junction, and when light strikes the cell there are many light induced electrons that are swept across to the end of the emitter to flow through the load.
I can't make sense of how these swept electrons travel through that gas of electrons already there, and why in open circuit there is a potential built across the cell if the gas of electrons is there, what makes the collected electrons different than the gas of electrons? I'm just not getting how the gas of electrons and collected electrons mesh together.

Can someone explain exactly how and why the rise in temp lowers Voc? I read the reverse saturation current lowers Voc, but its not really an answer that gives a detailed account step by step.

Finally, for recombination losses, it seems to me there is conflicting info, some sources speak of a fundamental absolutely required loss which i dont know how it actually works, and others simply mention a loss as the electron travels across the junction it can recombine with a slower moving hole, this loss being 10% of the incident power. Are they the same? What is the difference?
thanks

 

[Drakkith]

I can't make sense of how these swept electrons travel through that gas of electrons already there, and why in open circuit there is a potential built across the cell if the gas of electrons is there, what makes the collected electrons different than the gas of electrons? I'm just not getting how the gas of electrons and collected electrons mesh together.

My understanding as a non-expert:

Don't think of the electrons as being in a 'gas', but rather think of them as being in various energy levels, some of which are mobile and some of which aren't. The electron liberated when a photon creates an electron-hole pair is in the conduction band and is able to move quite easily around the material. While this electron exists and before it recombines with a hole, it contributes to an extra negative charge to one side of the PN junction, and many of these electrons combines from lots of light add up to generate a significant voltage, which is what you detect when you measure the open circuit voltage. The holes do the same thing on the other side of the junction, but with the opposite charge.

Can someone explain exactly how and why the rise in temp lowers Voc?

My limited understanding is that the higher temperature makes it easier for the electrons and holes to recombine by diffusing back against the electric field instead of going through the circuit. Since temperature is generally a measure of how hard particles are vibrating or moving around, a higher temperature gives the electrons and holes more energy to move against the field to recombine.

I can't answer your last question.

 

[Jman99]

Thanks, that all makes sense now about not thinking of them as gas, I never thought of it like.