The fascinating field of photovoltaics involves generating power with sand and the Sun. Capturing solar energy is the end result of complex chemical and physical processes.
Extracting Raw Silicon
As a first step, raw silicon is extracted from quartz for use in the photovoltaics industry. The semi-metal must be 99.99% pure to generate solar power. The photovoltaics industry utilizes the semiconducting properties of silicon in special ovens. Raw silicon is melted at temperatures of over 1,400 degrees centigrade. A thin rod known as the seed crystal is then submerged into the liquid silicon and pulled back up very slowly. During this process, the liquid silicon accumulates on the seed crystal and solidifies over four days, forming a silicon rod up to 2.8 meters in length.
Shaping the Ingot
This basic round crystal, known as an ingot, is now cut into a rectangular shape for purely practical reasons. Later on, square-shaped solar cells can be installed much more effectively on the surface of a solar module. The ingots are cut into millimeter-thin slices using a very fine wire saw. These individual slices, called wafers, form the basis of each solar cell. Once the wafers have been cut, they are sent through a wash tunnel, as even the smallest piece of dust or dirt can compromise solar cell production. The wafer surface is now very flat, just like a mirror, which causes many rays of light to be reflected and no longer used to generate power.
Preventing Reflection
To prevent this reflection, the surface is etched and roughened in a chemical bath. Under a microscope, one can see the resulting pyramid structure. This piling pyramid structure refracts light multiple times, allowing incoming light to be used far more effectively.
Adding the Phosphorus Layer
The next step in solar cell production is diffusion, where a negatively charged phosphorus layer is added to each wafer’s positively charged layer in an oven heated to some 900 degrees centigrade. Phosphorus atoms are injected with the help of nitrogen. The gaseous phosphorus-nitrogen mix is deposited on the wafer. At the interface between positive and negative charged layers, the free charge carriers created by the light are released, generating an electric current.
Creating the Grid Pattern
But how is the power generated in the individual cells transported? A stamp pack presses a silver alloy onto the front of the cells, creating the typical grid pattern. This silver coating ensures that the power can be transported later on. The solar cells are now complete and can generate and transfer power. However, each cell has a different level of electrical conductivity.
Evaluating and Sorting Cells
In a series of tests, the cell’s conductivity is evaluated and sorted. Following the test phase, the solar cells are assembled. The cells are soldered together in such a way that the voltage accumulates in a process referred to as lamination. The cells are assembled behind a pane of glass, protecting them from the elements for more than 25 years. One solar module contains 60 cells. When a number of modules are connected, a solar power plant is created, generating power from the Sun and the sand.
