PV Gap

Courtney Said:

Can someone give me a brief explanation on how solar panels are made and how they capture energy from the sun?

We Answered:

well first silicon is mined and poly or mono crystals are grown as large round slugs. These slugs are then cut wafer thin (a few mills thick) and connected via silver ribbons and then encased in a glass and aluminum frame.
Now believe me there is alot more to it, but that's the quick and easy explanation about how they are made.

The way they work is, when the photons in the suns rays hit the silicon crystals, electrons jump and an electrical charge is made.

Bonnie Said:

how are solar panels made?

We Answered:

Bob covered the normal processing behind single crystal silicon cells pretty well!


Thin film solar cells are made differently. Cadmium telluride is the second most common type of solar panel (and currently the cheapest on the market, so it's going to become even more important!), and you can't grow CdTe from the melt using Czochralski or Bridgman growth because it has a very small thermal conductivity and it won't freeze quickly enough into a crystal.




In our labs we used a mix of 'close spaced sublimation' (CSS) and 'RF sputtering'. You start with a sheet of glass with a transparent conducting oxide on it (you need this to carry away the electricity. Or you can just start with glass and sputter on the TCO).

After that, you need 2 layers of different materials to make the electrical junction: when you put them together they will make an electric field that will push electrons around.

First off we sputter or sublimate a thin later of CdS, followed by a thicker layer of CdTe (which is nearly always put on by CSS).

In sputtering you have a block of the purified material you want at the bottom, and a sheet of the substrate held above it. You fire a beam of argon ions at the material and it 'splashes' or 'sputters' (like when you drop a rock in water and the water flies everywhere). The substrate catches this material. Generally speaking this is a bit slow though.

In CSS you have a block of the purified material and you put the substrate above it. Then you heat the material until it goes from solid to gas. The substrate is cooler, so the temperature gradient drives the material towards it where it sticks and crystals can grow. This is much quicker than sputtering, and it's used by FirstSolar, one of the biggest solar power companies in the world.

In each of these cases you have to have the cell held inside a big system of pressure tubes etc.




CdTe cells have some weirdness; in order to make them work well you have to 'activate' them with chlorine. You can either heat them in a tank with a freon, or evaporate (which is like CSS) on a layer of cadmium chloride. You heat the cell and it reforms crystals around the Cl. After that you can put on your back contact: typically you 'etch' the back of the cell with an acid for 10-20s to make it tellurium rich so it's better at conducting electrons through to the wires. Then you might add a layer of arsenic telluride, which makes the cell more stable (and my results suggested that As2Te3 was a good material). Finally you can put on a contact; copper, gold or molybdenum are common.



Other methods used by other research groups we worked with include MOPVE - Metal Organic Vapour Phase Epitaxy:
http://en.wikipedia.org/wiki/MOVPE
...but the biggest CdTe company use CSS.

Victoria Said:

How are solar panels made?

We Answered:

Solar panels that make electricity directly from sunlight are arrays of solar cells. Solar cells are semiconductors; similar to computer chips but of simpler design, although making them still requires ultra pure materials and expensive, high tech equipment. Production also takes quite a bit of energy and produces toxic waste.