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!

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[@sadiomainmane829]

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

[@faraz2609]

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

[@debayanhalder7858]

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[@revenger3006]

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[@gameingplayer1352]

Great video

[@acetal5782]

Frfr

[@chamanlaldewangan6591]

Thanks sir. I understand the photovoltaic effect.

[@NkRai-hr8zf]

I can't understand led , photodiode and solar cell by reputed institutes, but you make it clear bro😊

[@Subhashree_Subudhi]

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

[@arvindsrivastav8066]

Sir You are an Amazing ! Teacher

[@A.venger_S]

You're voice and accent is so good and you explained it really well

[@Khan-xj9sp]

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[@neiltauro2234]

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[@aswin8063]

Now this is wat we call a legendary explanation

[@nehachoudhary672]

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[@kaceesnow]

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Topic is clearly and wisely explained 👌

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Amazing explanation!

[@prasenjeetfulmali6707]

Genuine explanation👍

[@premasantosh8436]

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.

[@sakethkashyapnagendra9278]

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[@MayankGoel447]

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[@riya...125]

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[@dr.lakshmimamilla9261]

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[@dr.abdelmounaimchetoui]

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U teach effectively, very appreciating.

[@ajayxoxo]

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[@hc8063]

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[@sewind6613]

Excellent explanation. Thank you so much.

[@natureClipsHimalayan]

best explanation, thank you 👏👏

[@ganeshraja1789]

Simple and superb

[@shaikrafik6300]

Thanks GOD

[@pradroydip]

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.

[@King-wp7yb]

I guess this is made for beginners,not for researchers

[@shaikjeelan4290]

Loved a lot.Thank You Sir

[@zoyanoor0039]

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

[@shubhanksingh6918]

lets say if Sir Issac newton would be watching you, then he would love this💗💗💗

[@hellobro564]

Newton doesn't know about semiconductors bruh

[@aryavbhola3066]

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

[@shafqatilyas971]

finally, I got the actual concept.

[@adityadivyasharma2969]

Thank you so much sir!!❤

[@kalyanitewari]

Thank you so much, sir!

[@svnspell6709]

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:/

[@athiramn]

Those which are already in the material are bound charges, both holes and electrons. And if they manage to reach the space charge region, they will be swept away by the electric field present there. This is limited by the equilibrium process of diffusion and built in potential. The carriers generated when light falls upon the junction are excited electrons with a specific life time, those which are generated at one diffusion length from the junction are, thus, swept away through the external circuit.

[@rukeshveera5608]

Thanks❤ great 👏 explanation

[@niranjan7457]

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?

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[@kaviyak683]

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

[@hrid._.42o]

Because of the strong polarity of depletion region

[@madhusudhany.v44]

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?

[@KhanAcademyIndiaEnglish]

Electric fields pull/push charges, just like how gravity pulls things.

[@niranjan7457]

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?

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It's too good 👍👍

[@JACARTISTEOFFICIEL]

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 ?

[@divyanshkumarsrivastava3325]

His name is Mahesh and he owns a channel Float Head Physics with even more beautiful content 0:03

[@johnsumith2107]

Sir please make lectures on structural analysis 🙏🙏🙏

[@cryptocheeze]

I wish i had seen this sooner❤

[@aryavbhola3066]

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.

[@shreyavijay715]

I have this SAME exact doubt!

[@gireeshbhat4158]

😆😅 If you attach a wire across diode, from one side electrons are leaving (from negitive side p) From another side of wire (from positive side n) electrons are coming So number of electrons outgoing=number electrons incoming what happens only charges get recombined if there is a separation there is potential Now tell me how electrons get finished 🤔

[@khayamdzanga3265]

You the best

[@zharaalipanahi8084]

Thanks 🙏🙏🙏🙏🙏🙏🙏🙏

[@niranjan7457]

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?

[@jothibaskarn887]

Very nice

[@riyagarai5805]

Great

[@vipyo489]

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?

[@standarsh7895]

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.

[@niranjan7457]

They are generated continuously because the light incident upon it, provides energy to the electrons, which get promoted to the higher energy level (this creates a free electron) and causes a hole to form (in the position where they had been initially before getting energy from the light)

[@subhradipsandilya1469]

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

[@inshaaabid5310]

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

[@AnjeshKumar-l3s]

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

[@my_oxyjin_bts_]

Charge carriers do not lie in either cb or vb, but they are somewhere in between the two bands aren't they? Bonded electrons lie in the vb and free electrons in the cb

[@ibtihajmujahid8206]

My question do they both hve drift current?

[@priyadharshini-px2vl]

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

[@rajatverma3085]

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[@tonyfalapatt1308]

Thankyou🤩🤩🤩🤩🤩🤩🤩

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Wooooow🙏🙏🙏

[@leavemealoneplease652]

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"

[@niranjan7457]

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?

[@KhanAcademyIndiaEnglish]

Yes pretty much on track :)

[@prasantaghora8831]

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

[@guts1303]

Yes current flows from left to right (opposite to flow of electrons and in the direction of the flow of holes)

[@satya4002]

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

[@mordecaichisata8131]

There is light in space, not just enough surfaces to reflect light on, that's why it seems dark in space.

[@niranjan7457]

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..

[@niranjan7457]

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?

[@vivekgudise3379]

Sir I do not find the photodiode video...

[@emohmomomo]

Solar cells are not biased right?

[@yoanshie]

They should provide notes damn

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[@thecerebrum.]

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[@mejiqal]

he dosent know what he explain

[@rimitejwa8827]

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