Photovoltaic modules are usually black or dark blue and this is due to the finish on the cell surface. We will clarify why the usual appearance in the modules has been like this for so many years.
Why are the modules mainly dark blue almost black?
It is known that the modules seek to trap as much light within the total incident spectrum as possible. For this reason, a product that has a dark colour means that it captures most of the light and reflects or lets out less light. Any dark colour tone facilitates this effect and in particular dark blue is the most clearly achieved.
And how do you obtain this almost black blue colour?
At the glass level, two factors come into play, but in this case, the glass must allow as much light to pass through, which is why it is transparent; and not letting out the light that is reflected internally.
- Roughness or surface texture of the glass
- Glass transparency
At the cell level, two factors also come into play, and in this case, the cell must absorb the greatest amount of light
- Cell surface texture
- ARC anti-reflective coating
It is at the cell level where we get the darkening effect and the blue colour. There are also low reflectivity glasses created with complex structures but they are of a very specific application in airports or similar.
How does each factor work at the cell level?
The blue colour is provided by the silicon nitride layer that is deposited on the cell surface. It is a very thin layer (nanometer thickness) that causes the optical effect of colour, that is, a surface that looks blue to the human eye means that it has trapped all the other colours of the incident light and only lets out the colour that We can see. In this case, it is interesting to catch the wavelengths closest to green, yellow and red in the case of silicon modules.
The surface texture is responsible for trapping as much light as reaches the cell’s surface. Let’s say it is what makes the product as dark as possible. Due to the characteristics of the cell, monocrystalline or polycrystalline, a homogeneous texture of pyramids (monocrystalline) or random (polycrystalline) can be made.
The texture in polycrystalline is more complicated and that is why there are many products on the market that are not textured, causing them to be lighter blue. Today almost all products are textured to improve their efficiency.
Why are there products with different shades of the blue cell to cell?
The different shades of blue in the same module do not affect its performance as they are caused by minimal changes in the thickness of the anti-reflective film on the cell. It is a merely aesthetic effect. From the factory, not only are the cells selected to have the same electrical performance, but the colours are also selected so that there are no significant colour jumps within the module. It is a meticulous job that our clients deserve.
Using the best technology improves product performance and is a direct benefit to the end owner.