Solar cells are used to capture solar energy and create electricity in most solar panels. The solar panels you most often see on homes and businesses, photovoltaic (PV) panels, all use solar cells. The cells are flat, dark-colored and shiny.
Most importantly, each cell contains everything necessary to transform sunlight directly into clean electricity. All the other components are used only to increase output and transform the electricity from DC to AC electricity.
Solar cell design
A solar cell is a complex and precise organization of many different materials. The topmost layer of solar cells consists of glass with an anti-reflective coat. The glass protects the materials underneath it, while the anti-reflective coat helps more sunlight reach the semiconductors. When you look at a solar cell, you will see a small grid pattern. This is a grid of thin metallic strips beneath the glass. The glass, anti-reflective coat and metallic strips create the top layer of the cell.
The middle layer of the solar cell is the most important section. It is where solar energy is created through the photovoltaic effect and consists of two layers of semiconductors. The first layer is made up of n-type material. This is generally silicon mixed with small amounts of phosphorous, which makes the silicon negatively charged. The second layer is a p-type material. This material is positively charged, and usually made by mixing silicon with small amounts of boron.
The bottom layer of the solar cell has two parts. There is a rear metallic electrode directly beneath the p-type semiconductor. This rear electrode works with the metallic grid in the top layer to create an electric current. The final layer is a reflective layer to reduce the loss of sunlight in the system. Different solar cells may use different materials depending on their intended use and desired cost. They may also have additional layers to those already mentioned. However, all solar cells use this basic configuration.
How a solar cell works
Let’s take a quick look at how a solar cell works. When sunlight shines on a solar cell, the light might be reflected, absorbed or pass right through it. Only the light absorbed by the semi-conducting materials can create electricity. The anti-reflective coating encourages less light to bounce off and the reflective backings encourage more light that would pass through to bounce back into the system instead. It is impossible to create a system that absorbs 100% of the light, but advancements are continuing to improve efficiency.
Once the light reaches the middle layer, the semiconductors absorb the light. Photons, tiny packets of energy contained within all light, then increase the energy within the atoms of the semiconductors. The n-type material contains excess electrons in the outer rings of its atoms. When it is energized, those electrons are knocked loose and immediately begin looking for something to bond with. The p-type material has holes in its atoms’ outer rings, meaning it needs more electrons to be complete. The freed electrons move to fill the holes.
Some of the electrons will immediately fill holes where the n- and p-layers meet, without creating any electricity. However, a barrier quickly forms. This is when the metallic grid on top and the rear metallic electrode of the solar cell become important. The metallic grid on top draws the free electrons from the n-layer toward it. The forced movement of these electrons in one direction creates an electric current. These electrons are then sent through an external circuit that uses an energy load to capture the electric current. Once that electricity is captured, the electron continues to move through the circuit until it reaches the rear electrode, which is near the p-layer. The electrons then fill the holes in the p-type material and the circuit is complete.
How solar cells are used in a home solar system
Each solar cell has the capacity to produce a specific amount of electricity. To increase electric output, many solar cells are connected to make a solar panel. Even though a solar panel is handled as one piece, every cell works independently. The solar panel collects the electricity from each cell.
Your house will require more than one solar panel to create enough electricity to meet your needs. When multiple solar panels are connected, it becomes a solar array. In a solar array, all of the electricity from each solar panel is sent through an inverter. The inverter transforms the DC electricity created by the solar cells into AC electricity, which you use in your home.
Although solar arrays are what you buy to power your home, it is the solar cells that do the most important work. The solar cells create electricity directly from the sunlight your house receives every day. Every other element of the solar array is only there to make this system more efficient and transform the DC into AC electricity. Without the unique design of solar cells, solar energy would not be possible.