We're now ready to talk about the next step in how silicon solar cells are made.

So in the last video, we talked about how we go from our base material, sand,

until the silicon material, the wafers we can use to create silicon solar cells.

So basically we talked about this bit of the production.

In this video, we'll move on and talked about how we actually form

the needed layers of the silicon solar cells and how we create the wires,

and how we end up in making solar modules.

Our starting material in the process is the p-doped wafer.

The p-doped wafer we get from the last tip, so basically during the crystal

formation we add elements that ensures that the wafer is p-doped.

The next step is Texturing, and let's have Hasmus explain why we need texturing.

>> You start with the silicon wafer that's approximately 180 micro metres thick.

And you texture so the standard texture in this wet chemical texturing.

So if we talk about monocrystalline cell,

it's a typically a potassium hydroxide or at least an alkaline path

it that edges these experiments on both sides of the wafer.

>> The reason we need the texturing is that it ensures better light traveling

inside the solar cell.

If we imagine we had a flat surface like this and

we looked at the incoming light.

We'd see a reflection loss because most of the light would just be reflected off.

Depending a little bit on which coding we have, we'd see some reflection loss here,

typically 10% after we apply to anti-reflective coating.

But the texturing achieves it's a pyramid like structure.

Like this.

When we have an incoming photon now, we'll again see a reflection.

But the reflection will typically end up hitting another pyramid and

we'll get it reflected back.

So this means we'll have a 10% loss for the first reflection and

then a 10% loss of that again, so it's only around 1% that gets reflected off.

So there are basically get two chances of entering the solar cell.

So this texturing is quite important for light traveling.

The next step in our process is n-doping.

So this is where we form the p-n junction.

>> We need to form p-n junction, so

that's basically the feature of a silicon cell that makes it a diode and

that makes it work as a solar cell, because we need a p-n junction

to say direct the current til when we create an electron hole.

Somewhere in the material, the electron will flow in one direction and

the hole in the other direction and we can collect these moving charge carriers on

both sides of the cell as a flowing current that we can extract and collect.

So the p-n junction is a very important part of the cell and typically we

produce it by, if we have a p type cell and we want to make an n type region close

typically on the front surface, we make the a phosporus diffusion.

So that means we take a batch of wafers into a tube furnace

with a phosphorus containing gas and at around 900 degrees,

phosphorous is diffused into the top micrometer so of the silicon.

>> With the p-n junction formed, we are ready to move on.

The next step is, of course, the enter Antireflective Coating.

As I mentioned before, the antireflective coating is really important,

because if we don't have an anti reflective coating,

too much of the light will just be reflected away from the solar cell.

>> Then we applied the antireflective coding,

the pcvd silicon nitrite, hydrogenated silicon nitrite,

75 nanometers typically on the front surface that makes the cell look blue.

>> With the antireflective coding in place,

the next step is across the contacting.

And the contacting is where we apply electrodes.

So, this is typically one of the things that we smooth recognizable

about the silicon solar cells.

So, we have these cross pass and we have these finger electrodes going across it.

So, this is basically our next step.

On the back side we coat aluminum.

>> We can screen print the front and rear contacts.

That's typically silver paste on the front,

that's optimized to edge through the antireflective coating and

create an isotomic contact to the underlying highly developed silicon.

And typically aluminum paste on the rear that makes a good contact to silicon,

but also dopes the rear side of the silicone p-type,

aluminum is a p-type doping to silicon.

And that means that we actually remove the phosphorus doped backside layer in

the same process and create a p-plus layer that's called the back-surface field.

And we have the middle contact, so that aluminum contact on the rear,

and there a silver contact, a grid, on the front.

>> With the front and rear electrodes in place, the last step is contact firing,

where we basically ensures that we get good contact,

and that we get this p-doping of the rear of the solar cell.

>> Both of these aluminum and silver contacts on front and

rear are then fired at high temperature.

That's why the paste difuses through and

into the silicon in some cases, and then creates a good contact.

And then in the end, we edge isolate the cell, so that there's no way

the current could run from front to back without going through the junction.

>> At this point, we arrive at a inverse sole like this,

a silicon solar cell wafer with the electrodes front and back, and

it's now ready to be assembled into a panel.

>> These cells may then be both, and

be contacted with ribbons to make strings of multiple

cells that are then connected to a panel that's to

be laminated with EVA to protect these cells.

And then with a protective glass and a aluminum frame you get

the final panel that can be installed in the field or on the roof.

>> For the panel fabrication, we now need to connect up the solar cells.

As you can see, the individual solar cells are here and they'll then

be connected front to back or back to front, then they go in through the module.

We'll then place it behind the glass screen and encapsulated with an EVA layer.

It'll all be placed in an aluminum frame and

then it's ready to be placed on a rooftop.

How are silicon solar cells fabricated

Introduction to solar cells

Meet the Instructors