Forward bias diode - Solar panel (1 Viewer)

[barbernator]

When a diode is forward biased, current is able to easily flow through it. ( N----> P within diode (electron flow direction)what textbook says )

When a solar cell is exposed to light and an external circuit, current is able to flow. ( P --> N within cell (electron flow direction) what textbook says )

Why, within the jacaranda textbook is electron flow in opposite directions for a solar panel and a forward biased diode. I have read over this like 50x and from my understanding of p-n junctions, they should both flow the same direction. I may be interpretting the textbook wrong, but I don't think I am. Also, I have definitely not got conventional current and electron flow mixed up.

any ideas?

 

[Bosanski Heroj]

Are you thinking of Page 239 Applications of Semi-conductors: Photovoltaic Cells ?

 

[barbernator]

Are you thinking of Page 239 Applications of Semi-conductors: Photovoltaic Cells ?

i have edition 2 :/

 

[barbernator]

ok i will rephrase my question.

Can someone please explain the electron flow direction within forward biased diodes and solar cells. Is the flow the same direction, or opposite and why?

 

[Bosanski Heroj]

http://hsc.csu.edu.au/physics/core/implementation/9_4_3/943net.html#net11

 

[barbernator]

http://hsc.csu.edu.au/physics/core/implementation/9_4_3/943net.html#net11

thanks for the help, but it doesn't resolve the dilemma

 

[dulip]

Our school told us that understanding them was beyond the course

but i'll try explain what I understand
So initially before photons hit the solar panel, the n type, on the top, is positively charged near the depletion zone as it is electron deficient. Similarly the region near the depletion zone in the p type is negatively charged. Now in the diagram there's an external circuit from the n type to the p type. When a photon hits, due to the photoelectric effect, the ionised electrons at the top of the n type will move through the external circuit towards the holes in the bottom of the ptype. Now as more photons hit, more electrons are seperated and move towards the ptype, this will make the N type MORE positive and the P type more negative. Thus the depletion zone is reduced and electrons flow from the P type to the N type and the circuit continues

does that make sense?

 

[barbernator]

Our school told us that understanding them was beyond the course

but i'll try explain what I understand
So initially before photons hit the solar panel, the n type, on the top, is positively charged near the depletion zone as it is electron deficient. Similarly the region near the depletion zone in the p type is negatively charged. Now in the diagram there's an external circuit from the n type to the p type. When a photon hits, due to the photoelectric effect, the ionised electrons at the top of the n type will move through the external circuit towards the holes in the bottom of the ptype. Now as more photons hit, more electrons are seperated and move towards the ptype, this will make the N type MORE positive and the P type more negative. Thus the depletion zone is reduced and electrons flow from the P type to the N type and the circuit continues

does that make sense?

i know how to explain the unidirectional flow of electrons within a solar panel, i just don't understand why the forward bias direction, when a PD is placed across a diode is in the opposite direction to the electron flow in a solar cell.

thanks for the explanation anyway

 

[Rathaen]

Um, I'm not overly sure about this, but from memeory forward bias is distinct from a solar cell because when you put a forward bias on a pn type semiconductor what you're actually doing is connecting the p-type side to a positive terminal and the n-type side to a negative terminal, and then placing a voltage across it. This attracts the electrons from the n-type to the p-type side (where the positive terminal is) and the holes from the p-type side to the n-type side, which basically squishes the depletion zone so that it becomes smaller and is easier for electrons to cross.

A solar cell works the way dulip explained with electrons in the valence band of the silicon atoms being excited into the conduction band and so on and travelling through the external circuit to reach the p-type side holes and vice versa.

The main difference is that in forward bias you are providing a voltage, and in a solar cell a voltage is generated by the photoelectric effect.

Hopefully this is correct, and hopefully it helps.

 

[Fizzy_Cyst]

I think I understand what you mean, I dont have a copy of the textbook in front of me so will try to explain.

In a diode, there is an external power supply. The electrons which flow through a diode originate from the power supply (hence travel from negative to positive terminal) -- forward biasing a diode, you connect the positive terminal to the p-type SC, hence electrons will flow out of negative terminal through N --> P then into positive terminal. The electrons are able to move from N --> P as the force due to the electric field trying to cause the electrons to 'drift' back to the N-side is smaller than the tendency of the electrons to redistribute themselves evenly under thermal motion

Whereas, In a solar cell, the electrons which flow through the external circuit originate from the P-N Junction. Seeing as the electric field in the depletion region is from N --> P, the liberated electrons flow opposite to the direction of the electric field and hence travel from P --> N.

Hope this answer suffices!

Do you by any chance