# How does solar panel turn light energy into electrical energy?

I’d like to present some basic concepts.

The solar panel is made of an electrically conducting material. The most important characteristic of a semiconductor are that electrons’ energy levels is not constant. There is a gap in between the two energies. This is similar to the image below.

Imagine electrons as water molecules. They may remain in the reservoir on the top of the hill or the river that is at the base of the hill. When the water molecule is transferred from the bottom to the top of the hill the water molecule is stored in some energy that can later be released when it flows to the hill’s bottom.

To make use of electrons instead of water as a medium storage for energy we’ll need to take two things at a minimum.

1: Giving an electron energy

Similar to how pumping water on the top of the hill provides water molecules a potential source of energy, an electron in the semiconductor (such like silicon) can absorb the energy that a photon transmits. The energy gap within the semiconductor acts as the elevation of the mountain. Fortunately, and the gap in energy is similar to light energy. I’m sure students in high school know that light can be thought of as particles and waves. Light with a wavelength of 450 nanometers is equivalent to particles and has a power of 1240/450 = 2.75 eV. For silicon the gap in energy is approximately 1.1 (eV). This means that a substantial amount of sunlight is taken up by silicon in order to move electrons at the bottom of the hill up to the top of the hill.

2. We need to be able to separate the pumped electrons

When electrons are pumped out from the bottom of the semiconductor, there’s an positive charged hole there. It is possible to imagine that positive charged electrons and negative charged holes have a love affair and are bound to meet and then recombine. If there’s no dam in the hilltop reservoir, water molecules will travel down the hill the exact way. Therefore, people construct an enclosure inside the semiconductor known as P-N junction.

The p-n junction forms a junction of n-type and type p-type semiconductors.

Pure silicon cannot carry charges due to its covalent bonds. When we add certain elements that have 5 electrons like P, free electrons are generated inside the silicon. The silicon in this instance conducts electrons’ charge and is referred to as the n-type. On the other hand Doping with B results in the p-type of silicon, where positively charged holes can be more larger than electrons.

When we join them there will be a an exchange of charge across the interface because the electron density in the two materials is different. A field of electrons is set up at the interface. The electric field will separate the pumped electrons and the resulting holes so that they do not mix.

This is a good example of what a solar panel does. It is my hope that I have explained in a way that students in high school can grasp.