Solar Cells? (1 Viewer)

[-X-]

They're pissing me off!

Can some one tell me if im understanding them correctly?

Heres how i understand it....

* Two layers of sem-conductors are used. One being an N-type and the other a P-type (N being on top).

* The e-s that are in the n-type are conducted by the metal grids and travel to a load returning back to the p-type semi-conductor.

* Light from the sun strikes the junction of the semi conductor causing e- to be freed from the p-type and travel to n-type semi-conductor. There are now holes left in p-type.

* The metal grids conducts the e-'s (current) and takes them to a load once again.

* From the load, they return back to the p-type waiting anxiously for another photon with enough energy to strike it.

* The electric field created in the junction causes e- to travel 1 direction only (to n-type).

-----------------

Well? right wrong? I did a search but confused me a little.

Thanks

 

[MyLuv]

Originally posted by -X-
They're pissing me off!

True I think this is right For dot points I think u can explain more:
- At 1st, n-p juntion have all hole filled with e prevent them to go from n to p.Then the 2 layers are connected by a metal grid ,e can flow from n to p through the metal...
...
-(last dot pt) The electric field cr8 by negative p juntion(recieved e from n) and poss. n juntion(+ hole by leaving e) make e flow from p to n

 

[inasero]

do we have to know applications of semiconductors? cant we just say in microchips and transistors?

 

[+:: $i[Q]u3 ::+]

you have to know how solar cells and photovoltaic devices work.. it's a separate dp.

(and u don't have to know how chips/transistors work.. u have to know how they impact society lol....)

 

[inasero]

hmm is that so....by PV devices do u mean to say the breathalyser?

cos if so ive gotta brush up on those sections dammit~

hey yewon can u explain SUCCINTLY how the solar panel works? cos jacaranda is really confusing~

 

[+:: $i[Q]u3 ::+]

hey how come i'm ill????? lol
um... i dunno how succinct i can be (-X- was pretty good)

- u got a layer of p-type silicon, then on top, a layer of n-type silicon. The n-type faces the sun, the p-type doesnt.
- sunlight hits the n-type, and electrons are released due to the photoelectric effect.
- a fine grid of metal contacts collect the electrons from the n-type silicon so u get an electric current.
- eventually, electrons are brought back to the p-type via the external circuit.
- electrons will then travel back through the junction-zone to the n-type silicon, and u start again. electrons only travel one way thru the zone.

 

[inasero]

ohhh...thank you for clarifying that

and btw my custom nick is in reference to your nick...which has always been somewhat of an enigma to me, inasmuch as my nick has been an enigma to others, including myself, so don't ask lol

 

[-X-]

Originally posted by +:: $i[Q]u3 ::+
u got a layer of p-type silicon, then on top, a layer of n-type silicon. The n-type faces the sun, the p-type doesnt.
- sunlight hits the n-type, and electrons are released due to the photoelectric effect.
- a fine grid of metal contacts collect the electrons from the n-type silicon so u get an electric current.
- eventually, electrons are brought back to the p-type via the external circuit.
- electrons will then travel back through the junction-zone to the n-type silicon, and u start again. electrons only travel one way thru the zone.

The difference between your explanation and mine is that with my explanation, once there are extra electrons in the ntype, they are emidiately conducted by the grid (no need for suns rays). However, When the electron returns to p-type from the load, it uses photoelectric effect to get to the n type (cause suns rays strike the junction).

Im not sure who is correct, at first i thought it worked like the way you explained it. After reading different textbooks, they seem to explain it differently, thats why i started this thread.


heh thanks for your replies BTW.

 

[ND]

Yeh the way i understood it was when the p-type and n-type come into contact, all the electrons from the n-type go to the holes in the p-type, leaving the n-type positive and the p-type negative. But then they say that when the photoelectric effect causes an electron hole pair causes an electron-hole pair to form on the n-type layer, the hole goes over the the p-type side (ok that makes sense, cos the p-type is negative), but then the electron goes around (through an external circuit) to the p-type too? I'd think the electron would be 'happy' with all the +ve charge around it. They said something about it wanting to pair back up with its hole, but still... if it's surrounded by +ve charges i don't see why it would move.

 

[Constip8edSkunk]

hmm...

theres a natural urge for the elctron to fill the holes, which is y the depetion zone appears in the first place. so if more holes a created greater that tendency becomes... but at the same time, the electric field also intensifies, so the electrons can only fill the holes in 1 direction, through the external circuit

and theres also elctrostatic repulsion between the electrons...

 

[+:: $i[Q]u3 ::+]

but the n-type layer is the side exposed to the sunlight.. (not the junction). It works cuz electrons are released by photoelectric effect (notice how solar cells don't work in the dark? haha.. usyd open day last year.. solar-powered car race and one of the cars stopped when it went in the shade.. ahh funny as.)

it's forced to go back into the n-type cuz of that.. bias-flow thing... (???)..

i'm sorry i don't know where i'm going with this... it's late... =P i've just finished a 4u paper and i swear i got back pains..

 

[Constip8edSkunk]

i think ND is saying why dun all the electrons conjugate at the n-type...



this pt is quite funny actually

jacaranda: light shines on n-type
longman: light shines on junction
macmillan: light shines on p-type

typical hsc science books

 

[+:: $i[Q]u3 ::+]

lol.. and the funny thing is, the textbook writers prolli all got it from the same source as well... shows how attentive they are.

 

[-X-]

Originally posted by Constip8edSkunk

jacaranda: light shines on n-type
longman: light shines on junction
macmillan: light shines on p-type

typical hsc science books

Nah i got jacaranda infront of me, it says light shines on juntion. If light shines on the junction then i think i got it correct. If it shines on n-type, then what +:: $i[Q]u3 ::+ is saying is correct.

Stupid textbooks, i dont think the writers understand it well either.

 

[+Po1ntDeXt3r+]

it falls on the p-n junction which is a neutral(?)
cos its like a sandwich...see HSC 01 and 02 (sucess one)
so becasue of the p-n junction

the n-type is +ve relative to the rest of the n-type and p-type is -ve relative to the rest of tht p-type
establishing an electric field.

photon causes the electron-hole pairs to 'break' up

the electric field of the p-type near the junction attracts holes and the n-type attracts e-..
with a net flow of charge a current is 'created'..

note: p-types are not +vely charged .. its called p-type because their charge carriers are holes
vice versa with n-type
source: Oxford phys dict

 

[ND]

Originally posted by Constip8edSkunk
hmm...

theres a natural urge for the elctron to fill the holes, which is y the depetion zone appears in the first place. so if more holes a created greater that tendency becomes... but at the same time, the electric field also intensifies, so the electrons can only fill the holes in 1 direction, through the external circuit

and theres also elctrostatic repulsion between the electrons...

So this 'natural urge' overcomes the natural +ve -ve attraction?
If this comes up in the exam i'll just have to fudge it.

 

[+:: $i[Q]u3 ::+]

Originally posted by +Po1ntDeXt3r+
it falls on the junction which is a neutral semiconductor..
cos its like a sandwich... hold on going to make one

ok back..
the electric field of the p-type attracts e- and the n-type attracts holes..
thats why in solar cells there is a 'mesh' like design which allows photons to pass thru.. for the top layer
source: Oxford phys dict

how can u have a neutral semiconductor?
bah. i'll fudge it in the exam.

 

[Constip8edSkunk]

Originally posted by ND
So this 'natural urge' overcomes the natural +ve -ve attraction?
If this comes up in the exam i'll just have to fudge it.

no the 2 forces reach an equilibrium i think, but only in 1 direction, the 1 opposing the electric field. but as theres no opposition in the other direction, the electrons are free to move that way.



neutral semiconductor as in all the holes are filled by electrons at the depletion zone?

 

[+Po1ntDeXt3r+]

oops
ok fixed up the first post.. sorri wasnt paying attention when answering... 'surfing 'books had a good explantion and also checked with sucess one and an engineer.. need way more sleep

Originally posted by +Po1ntDeXt3r+
it falls on the p-n junction which is a neutral(?)
cos its like a sandwich...see HSC 01 and 02 (sucess one)
so becasue of the p-n junction

the n-type is +ve relative to the rest of the n-type and p-type is -ve relative to the rest of tht p-type
establishing an electric field.

photon causes the electron-hole pairs to 'break' up

the electric field of the p-type near the junction attracts holes and the n-type attracts e-..
with a net flow of charge a current is 'created'..

note: p-types are not +vely charged .. its called p-type because their charge carriers are holes
vice versa with n-type
source: Oxford phys dict