Different Types of Solar Cells
As the world becomes more and more industrialized, the demand for energy has never been greater. And while fossil fuels have served us well for centuries, their days are numbered. The time has come to find a new way to power our lives, and that new way is solar energy.
Solar energy is clean, renewable, and available everywhere on Earth. It’s also inexhaustible – the amount of solar energy that hits Earth every day is enough to meet our needs many times over. In fact, according to some estimates, if we could capture just 1% of the solar radiation that reaches Earth’s surface, we could meet all of our global energy needs.
But capturing solar energy isn’t easy. Solar cells are one way to do it, and there are different types of solar cells available on the market today. Let’s take a closer look at three of the most common types: polycrystalline silicon cells, monocrystalline silicon cells, and thin-film solar cells.
Polycrystalline silicon cells
Polycrystalline silicon cells, also known as polysilicon or poly-Si, are made from a silicon wafer that has been cut into thin cells. The wafer is then heated to melt the silicon, and the resulting liquid is cooled to form a solid. The solidified silicon is then cut into thin cells that are arranged in a grid-like pattern. Polycrystalline silicon cells are typically used in solar panels and semiconductor devices. They are also used in some types of battery chargers and generators. Polycrystalline silicon cells have a number of advantages over other types of solar cells. They are less expensive to manufacture, and they are more efficient at converting sunlight into electrical energy. Additionally, polycrystalline silicon cells have a higher tolerance for heat and cold than other types of solar cells. As a result, they can be used in a wider range of climates.
Most Common Application of Polycrystalline silicon cells
Polycrystalline silicon cells are used in a variety of applications. They are commonly used to power solar panels, as well as other types of renewable energy systems. Polycrystalline silicon cells can also be used to charge batteries and provide backup power for off-grid homes or businesses. Additionally, polycrystalline silicon cells can be used to create electricity from the sun and wind, making them a popular choice for off-grid living. Some of the most common applications of polycrystalline silicon cells include:
- Residential and commercial solar panels
- Off-grid homes and businesses
- Portable battery chargers
- Solar thermal systems
- Wind turbines
- Electric vehicles
Monocrystalline silicon cells
Monocrystalline silicon cells are the most popular type of solar cell on the market today. They are also the most efficient, with a conversion efficiency of up to 22%. Monocrystalline cells are made from a single crystal of silicon, and they are cut from a silicon ingot in a cylindrical shape. The cylinders are then sliced into wafers that are just a few micrometers thick. Each wafer is then polished and etched to create the positive and negative electrodes. The cells are then coated with an anti-reflective layer to increase their light absorption efficiency. Finally, the cells are interconnected and packaged into a module. Monocrystalline silicon cells have a number of advantages over other types of solar cells, including their high efficiency and their stability over time. However, they are also more expensive to produce, and they require more precise manufacturing techniques.
Most Common Application of Monocrystalline silicon cells
Monocrystalline silicon cells are used in a variety of applications, including solar panels, electric vehicles, and other renewable energy systems. They are also used in some types of battery chargers and generators. Monocrystalline cells can be used to create electricity from the sun and wind, making them a popular choice for off-grid living. Some of the most common applications of monocrystalline silicon cells include:
- Residential and commercial solar panels
- Off-grid homes and businesses
- Electric vehicles
- Portable battery chargers
- Solar thermal systems
- Wind turbines
Common Types of Solar Cells
Solar cells contain materials with semiconducting properties in which their electrons become excited and turned into an electrical current when struck by sunlight. While there are dozens of variations of solar cells, the two most common types are those made of crystalline silicon (both monocrystalline and polycrystalline) and those made with what is called thin film technology.
Silicon Solar Cells
The majority of the solar cells on the market today are made of some type of silicon. by some estimates, 90% of all solar cells are made of silicon. However, silicon can take many different forms. Variations are most distinguished by the purity of the silicon, which refers to the way the silicon modules are aligned.
The greater the purity of the silicon molecules, the more efficient the solar cell is at converting sunlight into electricity. The majority of silicon-based solar cells on the market – about 95% – are made of crystalline silicon, making this the most common type of solar cell. But there are two types of crystalline: monocrystalline and polycrystalline.
Monocrystalline Silicon Solar Cells
Monocrystalline solar cells, also called single crystalline cells are easily recognizable by their coloring. But what makes them most unique is that they are considered to be made from a very pure type of silicon.
In the silicon world, the more pure the alignment of the molecules, the more efficient the material is at converting sunlight into electricity. In fact, monocrystalline solar cells are the most efficient of all; efficiencies have been documented at upwards of 20%.
Monocrystalline solar cells are made out of silicon ingots, a cylindrically shaped design that helps optimize performance. Essentially, designers cut four sides out of cylindrical ingots to make the silicon wafers that make up the monocrystalline panels. In this way, panels comprised of monocrystalline cells have rounded edges rather than being square, like other types of solar cells.
Beyond being most efficient in their output of electrical power, monocrystalline solar cells are also the most space-efficient. This is logical since you would need fewer cells per unit of electrical output. In this way, solar arrays made up of monocrystalline take up the least amount of space relative to their generation intensity.
Another advantage of monocrystalline cells is that they also last the longest of all types. Many manufacturers offer warranties of up to 25 years on these types of PV systems.
The superiority of the monocrystalline cells comes with a price tag. In fact, solar panels made of monocrystalline cells are the most expensive of all solar cells, so from an investment standpoint, polycrystalline and thin film cells are often the preferred choice for consumers. One of the reasons monocrystalline cells are so expensive is that the four-sided cutting process ends up wasting a lot of silicon, sometimes more than half.
Polycrystalline Solar Cells
Polycrystalline solar cells, also known as polysilicon and multi-silicon cells, were the first solar cells ever introduced to the industry, in 1981. Polycrystalline cells do not go through the cutting process used for monocrystalline cells. Instead, the silicon is melted and poured into a square mold, hence the square shape of polycrystalline. In this way, they’re much more affordable since hardly any silicon is wasted during the manufacturing process.
However, polycrystalline is less efficient than its monocrystalline cousin. Typically, polycrystalline solar PV systems operate at a 13-16% efficiency. again, this is because the material has a lower purity. Due to this reality, polycrystalline is less space-efficient, as well. One other drawback of polycrystalline is that it has a lower heat tolerance than monocrystalline, which means they don’t perform as efficiently in high temperatures.
Thin Film Solar Cells
Another up and coming type of solar cell is the thin film solar cell with growth rates of around 60% between 2002 to 2007. By 2011, the thin film solar cell industry represented approximately 5% of all cells on the market.
While many variations of thin film products exist, they typically achieve efficiencies of 7-13%. However, a lot of research and development is being put into thin film technologies and many scientists suspect efficiencies to climb as high as 16% in coming models.
Thin film solar cells are characterized by the various types of semiconducting materials (including silicon in some cases) that are layered on top of one another to create a series of thin films.
PV Solar Cell Construction
Solar cells are constructed of an upper layer of silicone containing negatively charged electrons (n-type) and a bottom layer of silicone containing positively charged electrons (p-type).
When the sun’s light (photons) hit these photovoltaic solar cells, electrons are released from the bottom layer of silicone and jump across to the upper layer of silicone causing current to flow and thus creating energy.
The more light that shines on these cells, the more electrons that jump up and the more energy that is produced. This is how solar cells work to continuously produce energy, but only when exposed to light.
How To Test PV Solar Cells
Testing PV cells to make sure they’re working properly.
Procedure For Testing Solar Cells
To test solar cells, you will need to place your solar cells in direct sunlight and use a multimeter that measures both Voltage and Amperage.
Testing For Volts
To test solar cells for the volts reading, make sure the multimeter is shut off. Plug the black (-) lead into the black port and the red lead into the V (voltage) port.
Turn on the multimeter. Set the dial of the multimeter to the volt position.
Put your solar cell down on a clean work area (preferably a block of wood) with the positive side facing up. (That’s the side without the tabs attached. facing up).
Touch the multimeter black lead to the solar panel’s negative contact (which is the tab wire coming from the underside of the solar cell.
Your voltage reading for a 1.75 watt solar cell should be about 0.5 volts. If the reading is much less, then this solar cell is most likely defective and you should not use it in your solar panel. If you are testing solar cells that are bigger, than your readings should obviously be bigger.
Testing For Amps
To test solar cells for the amp reading, make sure the multimeter is shut off. Plug the black (-) lead into the black port and the red lead into the A (amps) port.
Turn on the multimeter. Set the dial of the multimeter to the amps position.
Put the solar cell down on a clean work area (preferably a block of wood) with the positive side facing up. (That’s the side without the tabs attached. facing up).
- Touch the multimeter black lead to the solar panel’s negative contact (which is the tab wire coming from the underside of the solar cell).
- Touch the red lead to the solar cell’s positive contact (which is any contact point on the positive side of cell).
Your amperage reading for a 1.75 watt solar cell should be about 3.5 amps. If the reading is much less, then this solar cell is most likely defective and you should not use it in your solar panel.
So if you are using the same solar cells as we do in our examples, your volt, amp, and watt readings should be just under: 0.5 volts, 3.5 amps, and 1.75 watts.
Great, this solar cell is working correctly and can be used in your solar panel!
What are solar photovoltaic cells?
A solar module is made up of six different components, but arguably the most important one is the photovoltaic cell, which actually generates electricity. The conversion of sunlight, made up of particles called photons, into electrical energy by a solar cell is called the “photovoltaic effect”- hence why we refer to solar cells as “photovoltaic”, or PV for short.
A solar cell works in four generalized steps:
- Light is absorbed and knocks electrons loose
- Loose electrons flow, creating an electrical current
- The electrical current is captured and transferred to wires
The photovoltaic effect is a complicated process, but these three steps are the basic way that energy from the sun is converted into usable electricity by solar cells in solar panels. A PV cell is made of materials that can absorb photons from the sun and create an electron flow. When electrons are excited by photons, a flow of electricity known as a direct current is created. Below, we’ll dive into each of these steps in more detail:
PV cells absorb incoming sunlight
The photovoltaic effect starts with sunlight striking a photovoltaic cell. Solar cells are made of a semiconductor material, usually silicon, that is treated in such a way that allows it to interact with the photons that make up sunlight. The incoming light energy causes electrons in the silicon to be knocked loose and begin flowing together in a current, which will eventually become the solar electricity you can use in your home.
Electrons begin flowing, creating an electrical current
There are two layers of silicon used in photovoltaic technology, and each one is specially treated (known as “doping”) to create an electric field, meaning one side has a net positive charge and one has a net negative charge. This electric field acts as a diode and forces loosened electrons to flow through it in one direction, generating an electrical current.
Wires capture the electrical current and combine current from all cells of a solar panel
A photovoltaic cell on its own cannot produce enough usable electricity for more than a small electronic gadget. In order to produce the amount of energy a home might need, solar cells are wired together and installed on top of a substrate like metal or glass to create solar panels, which are installed in groups to form a solar power system. A typical residential solar panel with 60 cells combined might produce anywhere from 220 to over 400 watts of power.
Depending on factors like temperature, hours of sunlight, and electricity use, property owners will need a varying number of solar panels to produce enough energy. Regardless, installing a photovoltaic system will likely include several hundred solar photovoltaic cells working together to generate an electrical current. You can use the EnergySage Solar Calculator to get an idea of the savings you might see from a solar panel installation.
What are the main types of solar cells?
There are two main types of solar cells used today: monocrystalline and polycrystalline. While there are other ways to make PV cells (for example, thin-film cells, organic cells, or perovskites), monocrystalline and polycrystalline solar cells (which are made from the element silicon) are by far the most common residential and commercial options.
Silicon solar cells: monocrystalline and polycrystalline
Both monocrystalline and polycrystalline solar cells are initially made from silicon wafers. A monocrystalline solar cell is made from a single crystal of the element silicon. On the other hand, polycrystalline silicon solar cells are made by melting together many shards of silicon crystals.
This leads to two key differentiators between mono- and poly- cells. In terms of efficiency, monocrystalline solar cells are generally higher than their polycrystalline counterparts. This is due to the use of a single, aligned crystal of silicon, resulting in an easier flow for the electrons generated through the photovoltaic effect. Polycrystalline cells have shards of silicon aligned in many different directions which makes electricity flow slightly more difficult. However, solar modules made with polycrystalline solar cells are usually less expensive than monocrystalline options. This is because the manufacturing process for a polycrystalline cell is simpler and requires fewer specialized processes.
Thin-film solar cells
Thin-film solar cells are what they sound like: much slimmer, lighter-weight solar cells that are often flexible, while still remaining durable. There are four common materials used to make thin-film PV cells: Cadmium Telluride (CdTe), Amorphous Silicon (a-Si), Copper Indium Gallium Selenide (CIGS), and Gallium Arsenide (GaAs).
Thin-film solar cells are not nearly as popular as traditional crystalline silicon options for residential and commercial installations. Thin-film panels remain behind silicon panels in efficiency, and for most homes and businesses, this means they won’t be able to produce enough electricity from thin-film options. However, companies like First Solar have built entire businesses on producing panels with thin-film solar cells (in their instance, CdTe cells) for primarily large-scale utility power stations that aim to replace fossil fuel energy sources.
Organic solar cells
Solar panels made with organic solar cells are not commercially viable quite yet, but organic panels have many of the same benefits as thin-film panels. The biggest difference-maker for organic solar cells is their composition: while traditional and thin-film solar panels are made from silicon or other similar semiconductors, organic solar cells are made from carbon-based materials. They’re often referred to as “plastic solar cells” or “polymer solar cells” for this reason.
Organic solar cells are flexible, durable, and can even be made transparent. Heard of solar Windows? If they ever become a widespread product, they may very well be built with transparent organic solar cells.
Perovskite solar cells
Like organic solar cells, perovskites are not widely available yet. However, their low production costs and high potential efficiencies make them an intriguing option as the solar industry continues to expand and develop better and better solar production options.
How are solar cells made?
Most solar cells start as raw silicon, which is a naturally occurring element in several types of rocks. The first step in making any silicon solar cell is to extract the naturally occurring silicon from its hosts – often gravel or crushed quartz – and create pure silicon. This is done by heating the raw materials in a special furnace, and yields molten silicon that can then be further processed into monocrystalline silicon wafers for certain solar cells.
Once you have a polished and properly-sized silicon wafer (monocrystalline or polycrystalline), the doping process begins. When it comes to solar cells, doping yields two main regions within silicon: p-type silicon and n-type silicon. P-type silicon is made with boron, while n-type silicon is created with phosphorus.
Why make these two types of silicon? We won’t go into the scientific details too much, but in a nutshell, pure silicon is not a very good conductor of electricity. By adding boron and phosphorus to silicon wafers, an electron imbalance is introduced, creating an electric field at the intersection of the p-type and n-type silicon, also known as a p-n junction. By the way – the “p” in p-type stands for positive, and the “n” in n-type stands for negative. This is because p-type silicon is at an electron deficit, and n-type silicon has a surplus of electrons floating around. A simple way to think about the flow of electricity that makes solar cells work is that it’s just electrons flowing from the n-type silicon with extra electrons to the p-type silicon that doesn’t have enough.
After doping the silicon cells, there are a few more steps needed to make a complete solar cell. One of these steps is to apply an anti-reflective coating to the cell – this prevents incoming sunlight from simply bouncing off of the shiny wafer before the photons can interact with the silicon. Another step is to add metal contacts to the cells that will act as a conduction funnel for the electricity generation from the cell, connecting that current to the overall wiring and electrical systems of a full solar system.
Finally, cells are covered with a protective layer, usually glass. Once manufacturers have a single solar cell, they can combine them together to create actual solar panels that combine the power of 60 or more individual cells to generate a useful voltage and current.
The future of solar panel efficiency
The efficiency of a PV cell is the amount of electrical power that’s coming out of the cell compared to the energy from the light shining on it—this number demonstrates how effective the cell is at converting energy. And as mentioned, there are a variety of factors both internal and external to solar cells themselves, like light intensity and wavelength, that affect the conversion efficiency of a solar cell. There are a few main areas of development around improving solar cell technology:
Multijunction solar cells
One of these important factors of PV cells is the range of wavelengths of light the material (silicon, thin-film, perovskite, etc.) can absorb and convert to energy. Light is made up of photons vibrating at a wide range of wavelengths, and the wavelengths that match the absorbable range of a solar semiconductor (known as a bandgap) can be captured by that solar cell.
A strategy that is already helping to improve PV cell efficiency is layering multiple semiconductors together to make what are called “multijunction solar cells”. Each layer of a multijunction cell can have a different bandgap – meaning they will each absorb a different part of the solar spectrum, making better and more complete use of the sunlight than a traditional single-junction cell.
P-type cell improvements using gallium
Over time, silicon cells doped with boron naturally degrade as they continue to be exposed to sunlight. The reason for this degradation is fairly straightforward: the process of including impurities like boron to create p-type silicon also causes inclusions of other atoms. One such atom is oxygen – this is more or less unavoidable and comes from the physical tools used to refine silicon.
Unfortunately, oxygen chemically reacts with boron when exposed to sunlight, which causes small defects in the silicon cell and reduces power generation over time. One solution to this problem is to use an element besides boron that won’t bond to the oxygen impurities. Gallium, a naturally occurring metal element, is one such material that is already being used in solar panel manufacturing to solve the problem of cell degradation, and is leading to higher efficiencies for solar panels around the world.
History of Photovoltaic Technology
The PV effect was observed as early as 1839 by Alexandre Edmund Becquerel, and was the subject of scientific inquiry through the early twentieth century. In 1954, Bell Labs in the U.S. introduced the first solar PV device that produced a useable amount of electricity, and by 1958, solar cells were being used in a variety of small-scale scientific and commercial applications.
The energy crisis of the 1970s saw the beginning of major interest in using solar cells to produce electricity in homes and businesses, but prohibitive (nearly 30 times higher than the current price) made large-scale applications impractical.
Industry developments and research in the following years made PV devices more feasible and a cycle of increasing production and decreasing costs began which continues even today.
Costs of Solar Photovoltaics
Rapidly falling have made solar more affordable than ever. The average price of a completed PV system has dropped by 59 percent over the last decade.
For more information on the state of the solar PV market in the US, visit our solar industry data page.
The cost of PV has dropped dramatically as the industry has scaled up manufacturing and incrementally improved the technology with new materials. Installation costs have come down too with more experienced and trained installers. Globally, the U.S. has the third largest market for PV installations, and is continuing to rapidly grow.
Most modern solar cells are made from either crystalline silicon or thin-film semiconductor material. Silicon cells are more efficient at converting sunlight to electricity, but generally have higher manufacturing costs. Thin-film materials typically have lower efficiencies, but can be simpler and less costly to manufacture. A specialized category of solar cells. called multi-junction or tandem cells. are used in applications requiring very low weight and very high efficiencies, such as satellites and military applications. All types of PV systems are widely used today in a variety of applications.
There are thousands of individual photovoltaic panel models available today from hundreds of companies. Compare solar panels by their efficiency, power output, warranties, and more on EnergySage.