I'm quite certain a lot of you already know that I breath, drink, and eat Renewable Energy, especially Solar Energy. My LOVE for this alternative source of electricity & Energy is a deep one.
Annoyingly most users or potential users (especially science students or students who studied elementary Chemistry) of a Solar System who are technically laymen in this field, they have zero understanding on how the most important component in the entire list components that make up a Solar System (I don't mean that of the planets and universe 😂)
So I'm taking the time out to give a little exposè!!!
First off, what's that "most important" component of a Solar System???
If you guessed right, I owe you a free consultancy services when you plan to have your own Solar System installation. 😊😊
Yes, it's the Solar Module, a.k.a Solar Panels, a.k.a Photovoltaic Modules, a.k.a the big black rectangular shaped components you'd see on people's roofs 🤕.
So how does the Solar Module work???
Basically, the Solar Modules are majorly made up of Solar Cells which are in turn made up of Solar Wafers. So now that we've broken it down to Wafers, what are they made up of?
SEMICONDUCTORS!!!
Yes, every Solar Module you see out there is made up of Semiconductors.
Now here's where I need your rusty Chemistry knowledge. Remember the PERIODIC TABLE?? Consisting of all the Chemical elements in the world??
If you haven't recalled, then you likely need not continue reading 😄😄. I'm just joking, continue, you can get your friend who knows a bit about Chemistry and read further with them.
So below are few points to note:
1. Solar Panels are manufactured from Semiconductor elements, and we can find these in Group 4 & 14 elements, in essence elements with 4 Valence Electrons.
2. This means that they are neither perfect Conductors nor perfect Non-conductors, because it takes more energy for an element to either gain or lose 4 Valence Electrons.
3. The gaining or losing of electrons is what produces electricity. Basically, electricity flows in the opposite direction of flow of electrons.
4. Silicon & Germanium both Group 14 elements have been proven to be the best Semiconductors for producing Solar Modules, most preferably SILICONS.
5. Because Silicon is a Semiconductor, its chemical composition needs to be altered to make it a perfect conductor of electricity. This altering process is what we call "DOPING" 😂😂, or "Adding Impurities".
6. Remember that we need a final chemical composition that can either easily accept electrons or give out electrons. So this leaves us with using Group 3 & Group 5 elements for Doping.
7. For Group 3 elements, Boron & Gallium have been identified as perfect dopants. Preferably GALLIUM.
8. For Group 5 elements, Phosphorus & Arsenic have been identified as perfect dopants. Preferably PHOSPHORUS.
Remember the KLMN ELECTRONIC CONFIGURATION.
-i.e 2, 8, 18, 32...... pattern.
The last number on the right indicating the number of Valence Electrons ready for chemical reactions.
So Silicon has 14 atomic number;
So it's electronic configuration is:
2, 8, 4.......meaning it has 4 valance electrons.
If we dope this Silicon with a Gallium (Group 13 Element) which has 31 atomic number;
So Gallium’s electronic configuration is;
2, 8, 18, 3....meaning is has 3 Valence Electrons.
Combining both Si & Ga, we have the image below:
See the missing pair on the right side of the Gallium? That shows that the 3 valance electrons has been distributed across the 3 atoms of Silicons, and the 4th silicon atom cannot form a perfect Covalent bond with the Gallium. This uncompleted Covalent bond creates a room for the opposite of electrons, called HOLES. Holes means the Chemical composition (Crystal Lattice) has the room to accept 1 more external electron.
If we dope this Silicon with a Phosphorus (Group 15 Element) which has 15 atomic number;
So Phosphorus’ electronic configuration is;
2, 8, 5....meaning is has 5 Valence Electrons.
Combining both Si & P, we have the image below:
See that the Phosphorus atom created a perfect bond with Silicon atoms, leaving a spare electron. This means that the Crystal Lattice has one extra electron to give out.
So, for dopants (Gallium) that leave us with room to accept an extra electronic (absence of electron, which we in turn call HOLES), we call that P-Type Doping, and that of dopants (Phosphorus) that leaves us with an extra electron to be given out, we call that N-Type Doping.
Two Key Words to Noted.
- Electron — Presense of Electron, which means it can give out Electron.
- Holes — Absense of Electron, which means it can accept Electron.
So generally, when you a combined a P-Type Silicon with an N-Type silicon, you have what we call a P-N Junction which makes up the Solar Cells in a Solar Panel. Chemically, the extra electron for the N-Type side has the potential to move and fill up the Hole in the P-Type Silicon.
Naturally, the extra electron on the N-Type side does not have enough Energy to migrate to the hole in P-Type side, so therefore it needs an external force ( 😁😁 following Newton’s 1st Law of Motion, A body (electron) will continue to be in its states of rest/motion unless acted upon by an external force).
What is the external source needed?? 🌞 ☀️ 🌤 🌅 SUNLIGHT or SOLAR IRRADIATION.
See above image, and notice the middle section where (-) electrons have moved to the P-Type side, and (+) holes have moved to the N-Type side. The movement creates and electric field which in turns creates current flow in the opposite direction of electron flow.
Two notable areas/sides of the P-N Junction.
- Emitter/Absorber (the side facing the sunlight that absorbs the PHOTONS and also Emits the generated direct current from the P-N Junction). It can either be the P-Type side or the N-Type side.
- Bulk Region ( A combination of the Depletion Layer and the other side or the P-N Junction)
The P-N Junction produces electricity through what we call the PHOTOVOLTAIC effect. Which means PHOTOns from the Sunlight producing direct electric current (VOLTAIC).
Assuming we are dealing with a Solar Cell (P-N Junction) where the Emitter/Absorber side is the N-Type side, meaning the Bulk Region is heavily P-Type doped and the Absorber side is N-Type doped:
So once the photons from the sun hits the solar cell, it excites the extra electrons in the Absorber layer ejecting them towards the Bulk Region where they combine with the holes. These electrons that moves creates more holes which in turn combines with the nearest electrons, flowing through the closed circuit and finally returning through the positive terminal to recombine with a hole, ending that particular electron-hole pair.
This electron-hole pairing is what creates electron flow, which in turn creates current flow in the opposite direction.
This above description is what we now term as P-TYPE SOLAR CELL, because the Holes at the Bulk Region are the most active components.
The N-TYPE SOLAR PANELS would have its cell having a P-Type doped Emitter/Absorber side, and a heavily N-Type doped Bulk Region.
Same technique of photon exciting electrons. Typically we’d expect the photon to excite holes 😂, no way!!!…..The difference here is that, for every P-type doped silicon, there is always a tad amount of electrons present (we call this minority carriers). This is same with the earlier explained P-Type Solar Cell where the Absorber side is N-type doped, the minority carriers would holes at the Absorber side, but since we’re focusing on electron, we focused on it’s majority carriers.
In Essense:
N-Typed Doped Silicon = Electron is Majority Carriers, and Holes is Minority Carriers.
P-Type Doped Silicon = Electron is the Minority Carriers, and Holes is the Majority Carries.
So, for N-Type Solar Cell, the Electrons at the Bulk Region are the most active components.
References
- https://www.schoolsobservatory.org/learn/tech/instruments/inst_ccd/semiconductors
- http://science.babson.edu/winrich/semiconductors/acceptor.htm
- https://solarmagazine.com/solar-panels/n-type-vs-p-type-solar-panels/
- https://www.mks.com/n/diode-physics
- https://ieeexplore.ieee.org/document/6384087?arnumber=6384087