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What Is Monocrystalline Silicon in Photovoltaic Panels?

Monocrystalline silicon is the base material for silicon chips used in virtually all electronic equipment today. It is also used to make photovoltaic cells due to its ability to absorb radiation.

How does a Solar Panel Works: The S...
How does a Solar Panel Works: The Science Behind It
What is monocrystalline silicon in photovoltaic panels?

It is often called single-crystal silicon or in short mono c-Si or mono-Si.

This kind of silicon consists of silicon in which the crystal lattice of the entire solid is continuous. This crystal structure does not break at its edges and is free from any grain boundaries.

It can be prepared as:

  1. An intrinsic semiconductor that is composed only of very pure silicon

  2. It can also be doped by adding other elements such as boron or phosphorous.

Monocrystalline Silicon in Solar Panels

It is used to manufacture high-performance photovoltaic (PV) panels.

The quality requirements of monocrystalline solar panels are not very demanding. In this type of plate, the demands on structural imperfections are less high compared to other uses. For this reason, the lowest quality silicon is used.

Despite this, the monocrystalline silicon photovoltaic solar power industry has improved considerably.

How Is the Manufacture of Monocrystalline Silicon Solar Panels?

In addition to the low production rate, there are also concerns about wasted material in the manufacturing process.

Creating space-saving solar panels requires cutting the circular wafers into octagonal cells that can be packed together. Circular wafers are a product of cylindrical ingots formed through the Czochralski process.

The excess material is not used to create photovoltaic cells. It is discarded or recycled back to the production of ingots for melting.

These silicon cells can absorb most photons within 20 μm of the incident surface. However, limitations in the ingot sawing process mean that the commercial wafer thickness is generally around 200 µm.

Maintenance of Monocrystalline Solar Panels

If this kind of solar panels is dirty, can reduce their production. Hence the importance of keeping them clean. For this reason, we must carry out a cleaning service every so often.

During cleaning, we must avoid the use of abrasive detergents or cleaning tools that can damage the surface. Water should not contain large amounts of mineral salts that can stick to the surface. 

The procedure we must follow is to wet the panel with a lot of water. We do that until the dirt softens and thus avoid scratching the panel by sponging it to remove the dirt.

To do it better, it is important that you follow these tips:

  • Do not abuse detergents and make sure there are no traces left as it could damage the surface of our monocrystalline solar panels.

  • They should not be cleaned on windy days since it can carry dust and dirt.

  • We should avoid pressure washing.

What Is Its Efficiency?

This type of silicon has a recorded single-cell laboratory efficiency of 26.7%. This means it has the highest confirmed conversion efficiency of all commercial PV technologies.

The high efficiency is attributed to:

  • A lack of recombination sites in the single crystal

  • Better absorption of photons due to its black color. It is compared to the characteristic blue hue of poly-silicon.

Monocrystalline cells are more expensive than polycrystalline cells. For this reason, mono-Si cells are useful for applications where the main considerations are limitations of weight or available area.

This type of panel is used for example in spacecraft or satellites powered by solar energy. In these cases, moreover, efficiency can be further improved by combining other technologies, such as multilayer solar cells.

How Is Monocrystalline Silicon Produced?

Monocrystalline silicon is generally created by one of several methods.

This process normally takes place in an inert atmosphere, such as argon, and in an inert crucible, such as quartz. In this way, impurities that would affect the uniformity of the crystal are avoided.

Compared to polycrystalline ingot casting, its production is very slow and expensive. However, the demand for monocrystalline silicon continues to increase due to the superior electronic properties.

A silicon wafer is a thin slice of crystal semiconductor. It is such as a material made up of silicon crystal, which is circular in shape.

Usually, it is produced on a large-scale.

What Is the Czochralski Process?

The most common production method for monocrystalline silicon is the Czochralski process. This process consists of dipping a precision rod-mounted seed crystal into the molten silicon.

The Czochralski method is a method of crystal growth used to obtain single crystals of semiconductors, metals, salts, and synthetic gemstones.

The bar is then slowly pulled up and turned simultaneously. This allows us to get cylindrical ingot up to 2 meters long and weighing several hundred kgs.

Magnetic fields can also be applied to control and suppress turbulent flow, further enhancing the uniformity of crystallization. Ingot pulling is part of this process. 

The growth of a free surface accommodates volumetric expansion without major problems. This eliminates complications that could arise when the flux wets the container.

By this method, large single crystals can be obtained at high speeds. Currently, the diameter of the crystals can be varied by changing the thermal parameters. High crystal perfection can also be achieved.

What Other Manufacturing Methods Are There?

Other methods are:

The growth of the floating zone, which passes a polycrystalline silicon rod through a radio frequency heating coil. This coil creates a localized molten zone, from which a seed crystal ingot grows.

Bridgman's techniques move the crucible through a temperature gradient to cool it from the end of the container containing the seed. The solidified ingots are cut into thin sheets for further processing.

Monocrystalline Silicon in Electronics

Monocrystalline silicon is used in the production of semiconductor materials.

The factors that affect the electronic properties of the material are:

  • The amount of cellularization

  • Discontinuity

  • Micro defects

  • Foreign matter

  • Crystallographic defects

It would be impossible to manufacture transistor-based circuits without the perfect monocrystalline. This is why the electronics industry invests in plants to produce large single crystalline silicon.

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Published: September 3, 2018
Last review: August 30, 2020