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Anti-Reflection Coatings

Anti-reflection coatings on solar cells are similar to those used on other optical

equipment such as camera lenses. They consist of a thin layer of dielectric material,

with a specially chosen thickness so that interference effects in the coating cause the

wave reflected from the anti-reflection coating top surface to be out of phase with the

wave reflected from the semiconductor surfaces. These out-of-phase reflected waves

destructively interfere with one another, resulting in zero net reflected energy.

A critical passivating oxide thickness of about 300 was found to be important for

the design of these coatings. A new half-quarter-wavelength double layer

antireflection coating can be achieved with very low reflection if the passivating oxidehas to be thicker than this critical thickness.

Requirement of Anti-Reflective Coatings

For solar panels to be at their most effective they need to absorb as higher percentage

of the light they are exposed to as possible. It is the photons found in daylight that

generate electricity so it is important solar panels absorb the most photons they can. A

major problem is that the sun moves throughout the day so the angle of the lighthitting the panel changes. This often results in light being reflected off the panels.

Some solar panels are designed to move gradually throughout the day to track the

movement of the sun. This allows for an optimum angle to be maintained and

increases the light capture percentage. However, this is an expensive process. As a

result anti-reflective coatings have been touted as a more viable option.

The thickness of the anti-reflection coating is chosen so that the wavelength in thedielectric material is one quarter the wavelength of the incoming wave. For a quarter

wavelength anti-reflection coating of a transparent material with a refractive

index n1 and light incident on the coating with a free-space wavelength 0, the

thickness d1 which causes minimum reflection is calculated by:

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Anti-Reflective Coatings working

Untreated solar panels reflect around 68% of the light exposed to it. This means over

30% of the light, and potential electricity, is reflected away and lost. For increase solar

panels efficiency anti-reflective coatings are applied to the surface of the panels. The

coating is made of a thin film which is applied to the solar panel surface. Each surface

of this film reflects light but the degree of reflection between them varies 180 degrees.

This means the overall reflection is largely cancelled out and the solar panel is much

more efficient. Indeed, treated solar panels can absorb around 97% of the light they

are exposed to.

Improvement in Solar Cell by introducing Anti-Reflection Coating

Anti-reflective coatings are favoured over mechanical solar panels which move to

track the sun's movement. This is largely due to the fact the panels only need one

coating and very little maintenance afterwards. Solar panels which move with the sun

are more likely to break or become out of synchronisation. Even a slight deviation will

result in the solar panel's angle being at odds to the sun resulting in a loss of

absorption.

Solar panels to become a viable solution to our current energy crisis they need to be as

efficient as possible. Standard solar panels reflect away over a third of the light energy

they are exposed to. Anti-reflective coatings cancel out this reflection allowing for a

close to perfect absorption level. The ease of application and low price of this method

gives it a clear advantage over other technologies and can only be a good thing for the

future of solar energy.

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Magnolia Solar Corporation Work for Anti Reflection

Technique

The company's nanostructured Anti-Reflection coating allows for maximum solar

energy absorption for the complete solar spectrum covering Ultraviolet, Visible and

Infrared part of the solar energy. This approach allows for better than 95 percent of the

sun energy absorption and minimizes the reflection losses to less than approximately 5

percent. We believe this is a significant improvement over what is commercially

available today.

At normal sunlight incidence during peak sunlight hours, the reflection losses at the

glass-air interface have been reduced from approximately 4% to less than 1%. At large

angles of incidence during morning and late afternoon hours, the reflection losses

have been reduced from over 25% to less than 5%. We believe that the nanostructured

coating developed by Magnolia for photovoltaic applications can significantly

improve the performance of solar cells at all relevant wavelengths and incident angles

by reducing reflection losses.

Magnolia has filed multiple patents to protect its intellectual property and will

continue to make progress in further improvements to the AR coating technology for

other materials including Silicon, GaAs, and GaN and other materials of interest for

solar cell applications.