After the crystals pass quality control, they will then go to other partners who specialise in the application of different treatments and coatings. The most common is the anti-reflective coating, which is a film that is applied to the crystal to reduce the reflection of light and improve the view of the dial. Developed by the Ukrainian physicist Alexander Smakula in 1935 while he was working for the Carl Zeiss optics company in Germany, the technology was a German military secret during World War II.
A compound of aluminium oxide (Al2O3) magnesium fluoride (MgF2) and hafnium dioxide (HfO2) is heated to 1,800 degrees Fahrenheit in a vacuum. The compound melts and then evaporates into a gas and disperses throughout the chamber. When the gas comes into contact with the crystal it condenses on the surface. The process is basically the same as if you stand over a pan of boiling water with your glasses on; the water evaporates and condenses on the lenses. The only difference is that the steam disappears at room temperature, where the anti-reflective coating fixes at room temperature. The same process is used for adding the green or blue tint that is popular on some sapphire crystals, or an additional anti-scratch coating. Although the objective of the watch crystal is to provide an unobstructed view on the dial, most brands like to be able to see the crystal just slightly, this is why the coloured tinges are so popular. They don’t impede the visibility, but they are noticeable at certain angles.
Minimizing Reflections Increases Conversion Efficiency
Photovoltaic modules suffer from reduced conversion efficiency even before the sun’s light reaches the solar cell. This is because the solar module's protective glass cover reflects some of the incident sunlight. For typical glass panels, depending on the time of day 4% to 15+% of the incoming light is lost from reflections and thus, is not available to generate electricity. Applying an anti-reflective coating to the cover glass of the module will reduce these reflections and increase the module’s output power. Current commercial PV technologies convert 10%-20% of the incoming light to electricity. The same module with a suitable anti-reflective coating can deliver an additional 0.3%-0.6% power conversion. A product achieving higher conversion efficiency in a cost-effective manner can make solar modules more affordable.
What Makes an Anti-Reflective Coating Effective
An effective anti-reflective coating for solar module cover glass maximizes the light available to be converted to electrical energy. The optimum anti-reflective coating has the following capabilities:
Increases transmission over the entire solar spectrum
Increases transmission over the sun’s incident angles
Applicable for large surface areas at reasonable cost
