The Solar Sandwich - inside a solar panel

Have you ever wondered what makes up a solar panel? I like to think of it as being a bit like a silicon sandwich. Mmm. 

At its most basic, the panel is organised as above.

The top layer is the anti-reflection layer, which helps to stop the loss of light when it strikes the panel. This layer is typically made of silicon, tantalum or titanium oxide.

Now we get to the top junction, absorber and back junction layers. These energy conversion layers constitute the main part of the device.

The absorber is made of semiconducting materials. Semiconducting materials are those which strongly absorb visible radiation such as the photons from sunlight. The absorber absorbs the photons to its layer. 

The materials in the top junction and bottom junction are usually both made of silicon but one layer (the N-type silicon) has extra electrons and the other layer (the P-type silicon) has extra spaces for electrons called holes. 

Where the two types of silicon meet, the electrons scramble across the P/N silicon junction, leaving a positive charge on the P side and a negative charge on the N side. This also creates an electrical field. 

When the photons strike an electron or a hole with enough force, the electron or hole will become energised and move around. But instead of moving around randomly, due to the electrical field caused by the P/N silicon junction, the electrons move towards the N side and the holes move towards the P side.

The free moving electrons are then collected by thin metal fingers at the top of the cell, called the front electrical contact (we see these as a solar panel’s characteristic grid lines). From there, the electrons are put to work – e.g. powering a lightbulb or running your washing machine, before being sent to the back electrical contact layer, thus completing the circuit. 

Each silicon cell only produces half a volt, but if you string them together into modules, this can produce much more power. And when you arrange them together in an array, suddenly some, if not all of your electricity needs are taken care of*.

Et voila!

*Note, if you’d like to know how much energy you could be making through solar PV then we’d love to hear from you – https://solarsphereltd.co.uk/contact