Solar cells - working (and difference from photodiodes) | Semiconductors | Physics | Khan Academy 

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One of the clearest explanations of the photovoltaic effect. Well done !!! Perfect for educatory purposes. Complete enough also for engineering level!

Perfect presentation. Simplicity of reasoning behind explanaitions is exceptional. Best regards .

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Thank you much sir for clearing the doubt as i earlier thought that light falling on depletion region provides nothing, even when i studied the Photodiode. But now i realized that the depletion region even it is free of any carriers but they do contain the crystal atoms(Si along with the doped atoms which are bounded) and the atoms(acceptor/donor)which are still there are referred to here as the immobile free ions

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6:13 I also had this confusion but your explanation helped me alot... thanks 😊

Wonderfully explained ! Thanks a lot sir !!

Thankyou so much. Your explanation was very simply put , hence understood very well. In fact the best video lecture on semiconductors available. Very grateful for this sir.

All possible confusions can be cleared over here... Thank you 🙏

I never understood the concept until today Thanks. You're the Best

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amazing video. thanks for the great explanation

Thanks sir. I understand the photovoltaic effect.

Thankyou Very Much ❤️ We want you to cover more chapters of class 12 please. All the lectures of 11th were available and it was easy for me but now I am said as class 12th chapters are still not published whether it's chemistry or physics :(

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Excellent teaching...Thank You.

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Topic is clearly and wisely explained 👌

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Crystal clear explanation 👌 👏. Thank you somuch

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very well explained. Good job

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For a beginner it is okay, but that’s not a complete picture. There are so many concepts are missing, diffusion length for an instance. Formation of excitons within the diffusion length of the junction is critical for current collection.

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Thank you for the semiconductor series Khan Academy. This helped me a lot

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Amazing video! Wonderful ! Millions thanks ! By the way I have a question. How can it be possible that electrons get generated for years? Won't it finish just after some little hours ? If we don't use voltage that appears, does electrons get accumulated again and again? Finally what will be the effect on the cell ?

I wish i had seen this sooner❤

Great

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Very nice

finally, I got the actual concept.

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In your breakdown voltage video. i think because with increase in voltage as V=E.d, d will increase making E constant because charges are mobile but when the deplesion region covers the entire diode, d cannot exceed and furthur increase ibn voltage will lead to increase in electric field which in turn will lead to breakdown voltage. the only difference between your explaination and mine is that E will remain constant at first

Great!!! I have a question. If a cell is operating, electrons in depletion region will be decreased. Does 'life of solar cell' means losing enough electrons in depletion region that make the current?

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I want clarification that with p side we connect positive electrode or negative electrode in solar cell ???

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My question do they both hve drift current?

That is the difference between experienced teachers Thank you sir

Sir, can the electron-hole pairs that are separated in the depletion layer run out? I don’t understand where the holes and electrons keep coming from.

@khanacademy Isn't current supposed to flow from left to right in photodiode? It'll be great if you explain.

Can someone explain,why is it in the photodiode the majority charge carriers in N type (electrons) dont flow through the battery and recombine with the holes in p type,when we reverse biase it? Why is it that only the pair which was formed through photon gets to go through the battery and recombine on the other side? This might be a dumb question but if someone can explain,please do:/

Sir I do not find the photodiode video...

Sir,Why electrons move away towards corner instead of recombine with positive charge?you told it will swept away towards end due to electric field but why? However your explanation is best for my mindset because I always have doubts, questions just the way you explains. it's like you are answering exactly to my doubts, Thanks if possible clarify my doubt?

The fact is that what you call positive layer or negative layer are actually neutral charges then how can they conduct electricity.

can you help me find the video for photodiode and LED. i very badly need it . thank you

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please tell why these electrons wont get finished. some point in time they, all electrons must get differentiated. and now if we attach a wire across diode's ends and then remove it it must take away all electrons from -ve to +ve side would merge releasing energy and everything will get ionised.

There is no light ni space right! Then what is the use of sonar pannels in satelites ? Sir can you explain this

I understand that due to theke concetration on electron in n side and holes in p side, in behaves like a cell and if we connect with a bulb, in will glow. But, in a normal PN diode also, n side has higher concentration of electron and p side has higher concentration holes, then why in doesnt behave like a cell? If we connect a bulb across a normal PN diode, why theke bulb doesnot glow like a solar cell? Kindly clear my doubt plz...thanks

They should provide notes damn

Hi sir I need some clarification sir When Photon strike on depletion layer electron moves towards n side due to the hole (minority carrier) My question is In p side we have more holes than n side why electrons not moving towards p side? Kindly help me to clarify this

you are telling there is no charge carrier in CB and VB but how photon eject electron from VB?

This is called photovoltaic effects? Doesn’t it? 1.What would happen if electron-hole pairs generate outside of depletion region? Because light is also falling over the semiconductor diodes. 2. Does depletion layer increases(potential barriers increases) when it exposes to light? 3.how P-N semiconductor is made with figure? Specially depletion region? 4.light is exposed to the N-type semiconductor. In Practical, measures taken to increase the depletion layer by making N-types small in size compared to P-Type. ...... 5. When does diode work as forward biasing? Reverse biasing? 6. Oh,yes now I get that. Why was Sir teaching us that how visible light carries out electrons from semiconductor in room temperature? "Just automatic electrons will get out of semiconductor(must be doped either N-type or P-type) when it is exposed to Light"

Sir, at 04:59, you mentioned that the electrons will start repelling each other and hence cause a current to flow in the circuit However, these repulsions would have been there all the time, right? But since we now attached wires, a path for the electrons to flow has been created and hence, after the repulsion, they start flowing in the wire, which wasn't possible previously (When there was no path/wire for the electrons to flow and these electrons were moving within the diode itself after repulsion). Am I right sir?

Solar cells are not biased right?

Sir, one more doubt The only difference between solar cells and photodiodes is the voltage, right? And, can we use a photodiode for lighting up a bulb, because it can produce a current, right?

Sir you mentioned that the idea of a solar cell is to let the charges accumulate. But at 05:02, as soon as a bulb is connected, these charges start flowing and recombination takes place, thereby causing accumulation to cease (as told in 06:55 -> electron hole pairs are swept and allowed to recombine thereby recombination doesn't take place) If allowing the charges to recombine prevents accumulation, then how do charges get accumulated in Solar cells, even if there's recombination taking place?

Sir, at 05:10 You mentioned that as recombination continues, new electron - hole pairs form What is the relation between recombination and formation of new electron - hole pairs? Because doesn't the formation of electron - hole pairs depend on the light supplied? I assume that as recombination takes place (And thereby, electron - hole pair gets destroyed), there is a "Room" formed for the new electron - hole pair. Am I right in my understanding sir? So, I have an understanding that There is no drop in voltage, because for every electron - hole pair that gets destroyed, a new electron - hole pairs gets generated in the depletion region, get pulled and replace the destroyed electron - hole pair. Am I right sir?

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Sir another doubt... By shining light on the diode, we are creating electron - hole pairs. The electrons are pulled towards the N - type, while the holes are pulled towards the P - type And you mentioned that there is a voltage being created Is the voltage that is being created, in the depletion region (because holes that are generated in the depletion region, by photons, are pulled to the left and electrons that are generated in the depletion region, by photons, are pulled to the right, hence it appears as if there is a net current towards the left, in the depletion region), or outside it (because now that the holes have been pulled to the P type and electrons to the N type, where they are the major carriers respectively, doesn't it lead to an increase in the diffusion current [due to more availability of major charge carriers] which acts to the right) ? Kindly clarify sir..

Sir, Can we summarize the difference between solar cells and photodiodes, by saying that we allowed the charges to accumulate in solar cells and then attached wires after some time (in the time gap, charges accumulated because the light was shining on it) and the recombination process started only after some time, while we didn't give any time for charges to accumulate in photodiodes because we almost immediately reverse biased it, hence the recombination process started immediately, thereby allowing almost no voltage. The time for which photons were incident upon the diode is the factor that decides whether it is going to be a photo diode or solar cell. Am I right sir?

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Awesome. A suggestion, please don’t imitate an accent if not natural, it’s bugging for some. No offense.

he dosent know what he explain

You just need to correct your accent, otherwise everything is very nice, use Indian accent 🙂🙂🙂 , it's irritating to hear such kind of accent