What are Solar Cells and Solar Panels Made of?

Written-by

Janet Richardson

Reviewed-by

Richard Burdett-Gardiner

Updated on

Nov 24, 2024

What are Solar Cells and Solar Panels Made of?

A frequently asked question is what solar cells are actually made of, and how they are made. After all, solar panels themselves are made up of multiple solar cells, all of which work to absorb the sunlight and convert it into electricity. This page takes you through what solar cells are, how they are made, and the different materials that they can be made up of.

What Are Solar Cells?

Solar cells are also known as photovoltaic cells (PV), which work to generate electricity directly from sunlight. This is different from photovoltaic thermal cells (PVT), which work to provide heat for water in the home. Photovoltaic cells are connected electrically, and neatly organised into a large frame that is known as a solar panel. The actual solar cells are made of silicon semiconductors that absorb sunlight and then convert it into electricity.

A solar cell is a form of photoelectric cell and is made up of two types of semiconductors called the p-type and n-type silicon. The p-type silicon is created by adding atoms such as boron or gallium that have one less electron in their outer energy level than silicon. Due to boron having one less electron than is needed to form the bonds with the surrounding silicon atoms, an electron vacancy or “hole” is created. The n-type silicon is created by including atoms that have one more electron in their outer level than silicon, such as phosphorus. 

A solar cell consists of a layer of p-type silicon positioned next to a layer of n-type silicon. In the n-type layer, there is an excess of electrons, and in the p-type layer, there is an excess of positively charged holes. Near the junction of the two layers, the electrons on one side of the junction (n-type layer) move into the holes on the other side of the junction (p-type layer). This creates an area around the junction, called the depletion zone, in which the electrons fill the holes. 

When all the holes are loaded with electrons in the depletion zone, the p-type side of the depletion zone (where holes were initially present) now contains negatively charged ions, and the n-type side of the depletion zone (where electrons were present) contains positively charged ions. The presence of these oppositely charged ions creates an internal electric field that prevents electrons in the n-type layer from filling holes in the p-type layer.

The solar cell’s electrical characteristics, such as current, voltage, and resistance, vary when it is exposed to light. Individual solar cell devices are often the electrical building blocks of photovoltaic modules, known as "solar panels". 

The operation of a PV cell requires three different attributes:

The absorption of light:
The semiconductor material in a PV cell absorbs light energy and transfers it to electrons. Excitons (bound-electron hole pairs), unbound electron-hole pairs (via excitons), or plasmons are generated.

Separation of charge carriers:
The oppositely charged charge carriers are separated. 

Extraction of charge carriers: 
The separated charge carriers are extracted and sent to an external circuit. 

The type of material used in a solar cell can affect its performance. Gallium arsenide (GaAs), for example, performs very well because it has a favourable band gap, which helps with better absorption and reduced energy loss. Unfortunately, GaAs are expensive to produce and are mostly only used in space-based applications. 

You can calculate the efficiency of solar panels by dividing the panel power by the area of the panel and multiplying by 100. 

Currently, monocrystalline panels are the most efficient, with an efficiency of 15–22%. Polycrystalline panels are 15–20% efficient, and thin-film solar panels are 10–20% efficient. 

In most instances, solar panels that are used for domestic purposes are only able to take around 20% of the sunlight that they receive and turn it into electricity. There are several other forms of solar cells available that are used for commercial and industrial purposes. These can have an efficiency rating of up to 40%, but they do tend to be more expensive than domestic models.

One of the great things about solar technology is the fact that advances in the field are constantly being made, raising the overall quality and efficiency. It is expected that this will only increase with further research and development. Similarly, as these aspects increase, the price of solar panels is expected to keep falling – making them available to a much wider number of people. 

How Solar Cells are made

Stage One: Purifying the silicon The silicon dioxide is placed into an electric arc furnace. Next, a carbon arc is applied in order to release the oxygen. The resulting products are carbon dioxide and molten silicon. This will yield silicon that only has 1% impurity, which is useful in a number of industries. However, it is not yet pure enough for solar cells. The silicon, currently at 99% purity, is not purified even further using something called the floating zone technique. A rod of impure silicon is passed through a heated zone several times in the same direction. What the procedure does is drag the impurities towards one end with each pass. At a certain point, the silicon will be deemed pure, and the impure end will be removed.

Stage Two: Making single crystal silicon Solar cells are made from silicon boules. These are polycrystalline structures that have the atomic structure of a single crystal. The most commonly used method for the creation of the boule is known as the Czochralski method. During this process, a seed crystal of silicon is dipped into melted polycrystalline silicon. As the seed crystal is withdrawn, it is rotated, which means a cylindrical ingot, which is the boule, of silicon, is formed. The ingot is completely pure, as all impurities are left in the liquid.

Stage Three: Making silicon wafers Silicon wafers from the boule are sliced individually using a circular saw, the inner diameter of which cuts into the rod. A diamond saw is best for slicing, producing a cut that is as wide as the wafer. Around one-half of the silicon is lost from the boule to the finished circular wafer, although more can be lost if the wafer is cut into a rectangular or hexagonal shape. These shapes are sometimes used in solar cells because they can be fitted together perfectly, utilising all of the available space on the surface of the solar cell. Next, the wafers are polished to remove any saw marks, although some manufacturers have chosen to leave these marks as it has been found that rougher cells may absorb light more effectively.

Stage Four: Doping The most recent form of doping (also known as adding impurities to the silicon wafers) silicon with phosphorous is using a small particle accelerator to ‘shoot’ the phosphorous ions into the ingot. By controlling the speed of the ions, it becomes possible to control the depth of penetration. However, this new process has not yet been fully accepted. The traditional method tends to involve the introduction of a small amount of boron during the previous stage.

Stage Five: Placing electrical contacts Electrical contacts are used to connect each solar cell to the other, as well as to the receiver of the produced current. The contact needs to be incredibly thin so that they do not block any sunlight from being harnessed by the cell. Metals like palladium or copper are vacuum evaporated through a photoresist or deposited on the exposed portion of cells that have been partially covered with wax. After the contacts have been put in place, thin strips are placed between the cells. The most commonly used strips are tin-coated copper.

Stage Six: The anti-reflective coating Pure silicon is naturally shiny, allowing it to reflect up to 35 percent of the sunlight that hits it. In order to reduce the amount of sunlight that is lost, an anti-reflective coating is put onto the silicon wafer. The most commonly used types of coating are titanium dioxide and silicon oxide. The material that is used for the coating is either heated until its molecules boil off and travel to the silicon in order to condense, or the material undergoes sputtering. During this process, a high voltage will knock molecules off the material and deposit them onto the silicon and then deposit them onto the silicon at the opposite electrode.

Stage Seven: Encapsulating the cell The now finished solar cells are encapsulated. This means that they are sealed into silicon rubber or ethylene vinyl acetate. The encapsulated solar cells are then placed into an aluminium frame that has a Mylar or Tedlar back-sheet and a glass or plastic cover.
The Materials Found in Solar Cells

Here are the main materials that make up the solar cells in each panel.

Monocrystalline cells: Monocrystalline solar cells are made from single crystalline silicon. They have a distinctive appearance, usually characterized by a uniform colour, often black or dark blue. The cells themselves tend to have a square shape with rounded corners due to the way the wafers are cut from cylindrical silicon ingots. To keep the costs low and the performance at optimal levels, manufacturers cut the cylindrical silicon ingots into wafers and then trim the sides, resulting in their typical square shape with rounded corners. They tend to have the highest levels of efficiency and are considered the highest quality.

Polycrystalline Solar Cells: Polycrystalline solar panels were first introduced to the public in the early 1980s. Unlike their monocrystalline counterparts, polycrystalline cells do not require the silicon to be cut from cylindrical ingots, resulting in less waste. Instead, the silicon is melted and poured into square moulds, producing square cells. Polycrystalline solar panels are considered mid-range in terms of price and efficiency among the three main types of solar panels.

Thin Film Solar Cells: Thin film solar cells are manufactured by placing several thin layers of photovoltaic onto a substrate to create a module.

There are actually a few different types of thin film solar cells, and how they differ from each other comes down to the material used for the PV layers. The types are as follows:

• Amorphous silicon
• Cadmium telluride
• Copper indium gallium selenide
• Organic PV cells

Thin film solar cells are considered to be the cheapest option when it comes to solar panels, but they are also the least efficient. The efficiency rates for thin film solar cells can vary from 7% to 13% depending on the technology and materials that have been used to make them. In recent years, the popularity of thin film solar cells, and therefore the desire to know more about them, has taken a sharp increase. This also means that research and development for this form of solar panel have also increased. As a result, we can expect to see the efficiency rating increase in the coming years.

What are Solar Panels made of? 

Solar panels are made up of individual cells that are joined together. Though silicon is one of the most important materials used in solar panels, the materials that are used to manufacture solar cells are only one part of the solar panel itself. The manufacturing process combines six components to create a functioning solar panel. Here are the various components of a solar panel:

Silicon solar cells: 
Silicon is the most common semiconductor material used in solar cells, making up about 95% of modules sold today. It is the second most abundant material on Earth. The silicon solar cells are soldered together in a matrix-like structure between the glass panels, where they interact with the thin glass wafer sheet and create an electric charge.

Glass sheet: 
Most typical crystalline silicon solar panels are made of about 76% glass. The glass casing sheet is usually 6-7 millimetres thick, and although it is thin, it plays a significant role in protecting the silicon solar cells inside.
A standard solar panel includes a glass casing at the front to add durability and protection for the silicon photovoltaic (PV) cells. Under the glass exterior, the panel has a casing for insulation and a protective back sheet, which helps to limit heat loss and humidity inside the panel. The insulation is particularly important because temperature increases will reduce efficiency, which will result in a lower solar panel output. Solar PV manufacturers need to ensure that light is captured without overheating the technology.

Metal frame: 
A typical crystalline silicon solar panel is made of about 8% aluminium. A solar panel's metal frame protects the panel against inclement weather conditions or otherwise dangerous scenarios and helps mount the solar panel at the required angle.

Standard 12V wire
A 12V wire helps to regulate the amount of energy being transferred into your inverter, which in turn helps with the sustainability and efficiency of the solar module.

Bus wire
Bus wires are used to connect the silicon solar cells in parallel. They are covered in a thin layer for easy soldering but are thick enough to carry electrical currents.

Plastic polymer: 
A typical crystalline silicon solar panel is made of about 10% plastic polymer. 

Copper: 
A typical crystalline silicon solar panel is made of about 5% copper. 

Silver and other metals: 
A typical crystalline silicon solar panel is made of less than 0.1% silver and other metals. 

Boron and phosphorous: 
These are added to wafers during the manufacturing process. 

How are Solar Panels Manufactured?

Solar panels are made of monocrystalline or polycrystalline silicon solar cells soldered together and sealed under an anti-reflective glass cover. The photovoltaic effect starts once light hits the solar cells and creates electricity. The five crucial steps in making a solar panel are:

1. Building the solar cells

The primary components of a solar panel are its solar cells. P-type or n-type solar cells mix crystalline silicon, gallium, or boron to create silicon ingot. Once phosphorus is added to the mix, the cells can conduct electricity. At this point, the silicon ingot is cut into thin sheets and coated with an anti-reflective layer. Then, narrow slits are cut into the cells to funnel the flow of electricity.

2. Create a panel by soldering solar cells together 

When the phosphorus has been added the silicon wafers get their electrical charge, and metal connectors link each solar cell in a process called soldering. The number of cells soldered together depends on how big the solar panel is that is being manufactured. For reference, 60-cell panels are standard size, and 72-cell panels are generally used for commercial projects.

3. Install a back sheet, front glass layer, and frame

A back sheet is installed to the bottom of the solar cells for protection, usually made from an ultra-durable plastic material. Next, a thin glass sheet is placed on top of the solar cells to filter the sunshine into the solar cells. These components are held together by ethylene vinyl acetate (EVA) glue. All the parts are confined by a metal frame that latches onto mounting clamps on your roof.

4. Install the junction box

The junction box protects a solar panel's wiring from damage to keep the flow of electricity moving from the panel to its inverter, preventing electricity from reversing direction. This functionality is particularly essential because when a solar panel isn't producing electricity that panel will try to consume energy instead. The junction box doesn't permit any reversal of electric flow, so your solar panels can operate correctly.

5. Quality testing

Each solar panel ready to hit the market is assessed under Standard Test Conditions (STC) to make sure that the panels meet their projected outputs, efficiencies, and everything else the manufacturer promises in their technical specification sheet. These tests include electroluminescence imaging and performance tests under simulated sunlight conditions. Panels are put into a flash tester where "standard” conditions are simulated: 1000W/m2 irradiance, 25°C cell temperature, and an air mass of 1.5g. If it passes the standard tests, the solar panel is ready for shipment and installation.

6. Packaging and shipping

Panels that pass quality checks are labelled and certified for use, then packed and shipped to consumers and businesses. 

Want to Know More?

Have you found yourself interested in solar panels? If you're ready to move forward, head over to our directory of approved installation companies to find an installation company in your area. Alternatively, give us a call using the number at the top of this page.