Photovoltaic solar cells
Photovoltaic solar cell. Image: Dave Weaver Shutterstock

Solar energy is living better times, every day thousands of new solar panels are installed around the world, producing clean and free electricity. But, Do you know how cells or solar cells work? How are they able to generate electricity? We will tell you.

The sun is the most accessible energy on earth, but to convert it into electricity we need a very abundant element, sand.

It is necessary convert sand to silicon crystals with a purity of 99.999% if we want to use it in the manufacture of photovoltaic solar cells. To achieve this, the sand must undergo a complex purification process to obtain raw silicon (98% purity).

This raw silicon is made into a composite form of gaseous silicon, then mixed with hydrogen to obtain highly purified polysilicon. The process is a little more complicated if we want to obtain monocrystalline silicon, which is more expensive to produce but also with better performance.

This polycrystalline or monocrystalline silicon is molded to make wafers. These wafers are the central core of photovoltaic solar cells.

In this structure, the silicon atoms are linked together. We know that the electrons within this structure have no freedom of movement.

If we inject phosphorus atoms with 5 valence electrons into the structure, N-type doping, when sunlight hits the electrons, they gain photon energy, which makes them able to move freely. However, this random movement of electrons does not produce any current through the charge.

In order for electrons to move unidirectionally, a driving force is needed. A simple way to produce this driving force is with a PN joint.

How does a PN junction produce driving force?

If we inject boron with 3 valence electrons into pure silicon, there will be a hole for each atom. This is called P-type doping. If the two types of doped materials join together, some electrons on the N side will go to the P region and fill the available holes. This is how a impoverishment region, where there are no free electrons and no holes.

Through the migration of electrons, the N side becomes positively charged and the P side becomes negatively charged, which will form an electric field between the charges. This electric field produces the necessary motive force.

When the light falls on the N region, it enters the depletion region, where electrons and holes are produced which are repelled towards the N and P regions respectively by the electric field. The concentration of electrons in the N region and holes in the P region becomes so high that a potential difference will occur between them.

Operation of the solar cell. Image: Studio BKK Shutterstock

Now, if we connect a charge between these two regions, electrons will start to flow through the charge, combining with the holes in the P region, producing electricity.

In commercial solar cells, to increase energy efficiency, the N layer is very thin and very bulging, while the lower P layer is thicker and lightly doped, which increases the thickness of the depletion region and therefore electricity production.

Solar panel parts. Image: Alejo Miranda Shutterstock

Solar cells form solar panels by connecting a number of them both in series and in parallel, through copper unions.