Clarification on semiconductor physics in solar cells

[dacruick]

So, I am doing a little bit of research on how energy is created in solar cells. From what I understand, there is just a whole bunch of n and p junctions connected to each other electrons flow the same way. Or, electrons travel one way, and holes travel the other. So when you dope the silicon with say boron and phosphorus, what you are doing is creating a neutral system, but one side has electrons to give, and one side has electrons to take(holes). When electrons jump from the n-cell to the p-cell, the entire system remains neutral but there is an electric field created at the junction between the n and p cells. Is the energy then created by accelerating electrons across a potential??

And, say that there are, for the sake of simplicity, 100 free electrons. Once you accelerate them 'uphill' where do they go, and where do the electrons that continue to be accelerated come from?

And finally, I have a bunch of questions about band gaps and energy.

1) is the band gap the energy difference between the valence band and the conduction band?
2) does the conduction band conduct electricity by flowing electrons, and the valence band conducts electricity through the lack of electrons(otherwise known as holes)?
3)If I use materials to make this band gap smaller, I would essentially be increasing the amount of electrons that jump from the valence band to the conduction band, but also decreasing the potential created by accelerating the electrons through the field?
4) I read that they dope with boron and phosphorus often in very very small ratios. Sometimes parts per billion. What is the reason that doping with more holes and more electrons isn't more efficient? Is it related to the amount of energy coming from the sun's photons? If there were more holes and more electrons, would they just be sitting there because not enough photons are hitting the cell?

I realize I am asking a lot, and if you can only answer a couple questions, or even point out some flaws in my logic please do. Thank you

dacruick

 

[Valerie Park]

1) Yes, the band gap is the energy difference between the valence band and the conduction band.2) Yes, the conduction band conducts electricity by flowing electrons, and the valence band conducts electricity through the lack of electrons (otherwise known as holes).3) If you use materials to make the band gap smaller, you would essentially be increasing the number of electrons that jump from the valence band to the conduction band, but also decreasing the potential created by accelerating the electrons through the field.4) Doping with more holes and more electrons is not more efficient because it can reduce the amount of light absorbed by the cell which reduces the amount of energy generated. Additionally, doping with too many electrons or holes can lead to recombination of the electrons and holes, leading to a decrease in efficiency. The amount of photons hitting the cell does play a role in how efficient the cell is, but doping with the correct ratios of holes and electrons is important for maximizing efficiency.