By S.J. Watson



Inside the Solar Cell

One way to picture the workings of a solar cell it is to consider an interstate at rush hour. Picture this, the whistle sounds, the hour chimes, workers punch their time cards and start their engines for the trip home. The interstate start to fill up as all the vehicles are moving the direction of their lane, they weave in and around traffic as it varies in speed and as vehicles go on and off at exits. There is a constant flow of vehicles; trees and debris by the side of the road feel a constant breeze. The trigger for all the traffic at rush hour is time, the effect is wind. Now picture atoms with their electrons, the sun hits, the electrons start moving. The electrons want to find holes to fit into, it looks like the interstate. The constant flow of electrons is the current. Their trigger is the sun.

A solar cell is made of a semiconductor. If you look at some versions of a Periodic Table of elements the semiconductors are identified with a different color. Semiconductors let their outer shell electrons go when just a little energy is applied. Notice that silicon is in this group, silicon is what the majority of today’s solar cells are made of. The first time the solar effect was noticed selenium was used, notice it too is in the semiconductor grouping. Also in this semiconductor grouping is boron, in the column to the left of silicon, and phosphorus, to the right of silicon. Just a little bit of these two elements are put into the silicon of the solar cell to make intentional holes and extras so that electrons will flow.

There are two layers of a solar cell. One layer has the silicon/boron semiconductors and is the p-type, the electron poor side. The other layer is the silicon/phosphorus semiconductor and is the n-type, the electron rich side. Where the two layers meet is the p-n junction. Wires are connected on each side such that when the sun hits it the electrons start flowing and a complete circuit is present. All this motion has to do with electrons wanting to find a home; the atoms want full and thereby stable outer electron shells.

The wires that are connected to the solar cell can go to your lights, calculators, or batteries. The more solar cells, the bigger the solar cell, or the more efficient the solar will determine how much current is produced. The relation between the direction of the sun and the solar cell determines whether electron flow is present or not. Unlike batteries with cells that eventually stop working, solar cells continue to work unless broken by other external factors. Unfortunately, solar cells do not store electricity, when the sun shines they are on and the current flows. This is just like the wires of our homes, when we turn on a device the current flows.

Now if you understand the way the solar cell works you can expand to the diode and transistor. The same semiconductor p-n junction concept is used in the making of them. The discovery of all three, solar cells, diodes, and transistors, have their roots in the application of semiconductors. Diodes and transistors enabled the transition from the vacuum tubes of early televisions and radios into the lightweight and streamlined versions we have today. Not to be overlooked is their application in calculators and computers.

Why learn about the semiconductors and the working of the solar cell? Hopefully, with a little understanding of this concept, upgrading to solar lighting or taking on installation of solar panels will not be so intimidating. Remember that the solar cell is used for producing current, the flow of electrons. Passive solar energy is just heat, which is good for water applications, which is another article.

Educating and motivating people to be responsible financially and environmentally are some of the goals of S. J. Watson. She believes in promoting things that will help people’s quality of life. This interest is demonstrated in her involvement in solarmidnightoil.com, which promotes not only solar energy, but also aolar lighting, and alternative energy.