What is the Advantage and Disadvantage of PERC PV Module

In the never-ending quest for increased solar panel efficiency, materials engineers try a lot of different things to make photovoltaic cells turn solar energy into as much electricity as possible. 

For more information, please visit our website.

One of the most important and mature technologies to do that is through something called PERC, which stands for &#;Passivated Emitter and Rear Contact&#;, and is also sometimes called &#;Passivated Emitter and Rear Cell.&#; 

Most people don&#;t really have a reason to care about PERC, but what&#;s important to know is that, until recently, it was the most popular way to manufacture solar cells. PERC technology is a simple and cost-effective way to make more power from the same amount of space, but most manufacturers have moved on to a new technology called TOPCon. 

If you&#;ve gotten a quote from a solar installer and are choosing between different solar panels and price points, you might be interested to know about how high-efficiency PERC solar panels compare to other varieties of solar panels. 

What are PERC solar cells?

PERC is a technology which is used to improve the efficiency of solar cells by capturing as many extra photons as possible without fundamentally changing how a solar cell works. 

In ordinary crystalline silicon solar cells, electricity is produced when photons hit a layer of silicon, knocking electrons loose and then directed to flow along a wire. In general, modern monocrystalline silicon solar cells can convert about 20-25% of the incoming photons to electricity, but some photons pass through the silicon material without exciting electrons. 

When these cells are built into a solar module, the unconverted photons can hit the aluminum back layer and turn into heat, which reduces cell efficiency. Other photons excite electrons that end up getting recombined without flowing through the cell&#;s wires, meaning they don&#;t generate electricity. 

Typical silicon solar cells 

The diagram below shows a cross section of a typical solar cell built into a module. These are the layers, from top to bottom:

• Front contact

• Anti-reflective glass

• Negative (n-type) silicon layer

• Positive (p-type) silicon layer

• Back surface field (BSF)

• Rear contact

PERC solar cells 

To make a PERC solar cell, a manufacturer takes standard monocrystalline silicon cells and adds a passivation layer to the back that is designed to reflect photons back through the silicon layer. The cells are then micro-etched with chemicals or a laser to cut through the passivation layer so that the back contacts can reach it. A dielectric capping layer is added over the passivation layer to insulate the solar cell.  

When built into a solar module, the passivation and capping layers prevent electrons from hitting the back contact on top of which the cells are laid. PERC cell technology makes it so that more photons are captured by the silicon, meaning each cell makes a little more electricity than it would without the PERC layers. The maximum efficiency of PERC cells is about 23%, compared to about 21% for traditional monocrystalline silicon cells.

The diagram below shows a cross section of a PERC solar cell built into a module. These are the layers, from top to bottom:

• Front contact

• Anti-reflective glass

• Negative (n-type) silicon layer

• Positive (p-type) silicon layer

• Local back surface fields

• Passivation layer

• Dielectric capping layer

• Rear contact

Pros and cons of PERC technology

Pros

Cons

Increased efficiency

Could be subject to Light-Induced Degradation (LID)

Helps decrease heat in solar modules

Could be subject to Potential-Induced Degradation (PID)

Easy to produce

PERC technology is not a new technology, having been invented in by Australian scientist Martin Green and his team at the University of New South Wales. 

But commercially-available PV modules built using PERC solar cell technology are relatively new because materials scientists had to solve some problems before bringing the technology to market.

Pros 

As we described above, PERC technology reflects photons back into the silicon layers, causing the cell to produce more power and preventing electron recombination. These two benefits result in increased energy conversion efficiency and decreased heat in solar modules. They also ensure the cells work better in low light by producing meaningful voltage with less light than standard solar cells. 

Finally, PERC solar cells are relatively easy to make because manufacturers can use almost all of the same equipment and materials they use to make less-efficient solar cells. PERC technology can be added to both mono and polysilicon solar cells, and works well in bifacial applications, as well.

This ease of manufacturing has resulted in a sharp increase in PERC cell production since , and according to German mechanical engineering trade group VDMA, mono PERC and similar technologies accounted for over 60% of the global PV cell marketplace by as of .

Cons 

The cons of PERC solar cells have largely been mitigated in recent years, but it is important to point out why PERC didn&#;t catch on in the &#;80s when it was first invented. Chief among the concerns with this technology is a problem called Light-Induced Degradation (LID), which occurs in all silicon solar cells, but can be especially pronounced in PERC cells. 

LID occurs when boron from the positive silicon layer and oxygen mix, and usually results in a small, immediate reduction in power generation capability. This problem can be worse in PERC cells, which usually have extra boron, but all companies that produce and use PERC cells have come up with ways to fight it. 

Another type of problem that can occur in all silicon solar cells is called Potential-Induced Degradation (PID), which can happen when a difference in potential energy exists between the cells and materials of a solar module and the ground. 

It&#;s very complicated, but there is an international standard for module construction that manufacturers can follow, and all manufacturers worth their salt have implemented their own steps against PID. 

Your best bet is to choose a high-quality solar module manufacturer and read about the steps they take to mitigate PID and LID.

Who makes PERC solar panels?

Many solar module manufacturers use PERC solar cells in some of their products. Among the best of these are:

What are the alternatives to PERC technology?

PERC is one of the easiest and most cost-effective ways solar cell engineers have found to improve the efficiency and performance of solar cells. 

As we discussed above, the technology does have its drawbacks, and overcoming them is not a trivial matter. PERC is also a relatively mature technology, and it can&#;t be used to push efficiency much higher than existing top-of-the-line cells. 

That&#;s why many solar manufacturers are using alternatives to PERC that each have their own benefits and drawbacks. Here&#;s a quick rundown of other mainstream technologies currently used to increase solar cell efficiency: Tunnel Oxide Passivated Contact, heterojunction, and perovskites. 

Tunnel Oxide Passivated Contact (TOPCon) 

There&#;s that word &#;passivated&#; again. In fact, TOPCON technology is basically just the next generation of PERC, and like its forbear, it can be added to cells manufactured in the traditional way. TOPCon involves adding an ultra-thin layer of silicon dioxide (SiO2) and a layer of polycrystalline silicon doped with phosphorus. 

Because TOPCon is the next logical step after PERC, it does not add a great deal of additional cost to the finished product. It can produce additional gains in efficiency over PERC, but its theoretical maximum efficiency is 23.7%. It&#;s important to note that modules manufactured with current TOPCon technology top out at around 23%, though. 

Heterojunction (HJT) 

Heterojunction solar cells are made of alternating layers of traditional crystalline silicon and amorphous silicon, the latter of which is normally associated with thin-film solar panels. By combining the two different kinds of layers, HJT cells absorb more wavelengths of light, and the different layers work together to make the cells the most efficient on the market today. 

Unfortunately, HJT technology cannot be made in the same way traditional solar cells can, so it requires significant re-tooling and new industrial processes. This tends to make HJT solar modules quite expensive, although they do carry a reputation for premium quality and high performance. 

HJT solar cells have a theoretical maximum efficiency of greater than 26.7%, but current offerings from companies like REC Solar and Panasonic top out around 24%.

Perovskites 

Perhaps the most exciting and furthest-off technology to improve the efficiency of solar cells is called perovskites. 

Perovskites are a class of materials that have a certain crystalline structure that makes it extremely easy to produce and carry electrical charges in photovoltaic applications. This characteristic means perovskite solar cells could eventually have a conversion efficiency as high as 38%.

Unfortunately, many naturally-occurring perovskites contain lead, which is toxic. Safe artificial perovskites have been created using tin, but they are very difficult to work with and degrade much faster than their lead-based cousins. 

Oxford PV, the world&#;s leading perovskite solar cell manufacturer, has created &#;tandem cells&#; by embedding a layer of perovskites on top of traditional silicon solar cells. These cells set a world record for efficiency of 29.52% in December of . Oxford PV hopes to sell its products to the residential market starting in . 

Goto KINGSUN to know more.

Additional reading:
The Benefits of Using 72 Cells Solar Panel Factory

If they can pull it off at a reasonable price, they might make PERC, HJT, and all the other technologies seem like old news. 

The final word on PERC

If you&#;re a homeowner in the USA who has been looking for quotes for solar, you&#;ll probably get at least one quote that includes PERC solar panels. 

As we&#;ve discussed above, these panels are likely to be more efficient than traditional solar panels, which means they&#;ll produce more electricity in the same surface area. If maximizing your roof&#;s potential for energy generation is important to you, modern PERC solar panels from a top manufacturer will be one of your best option

To help you narrow it down, we have a side by side comparison of popular two popular brands that offer PERC technology. Read here for more information: Qcells vs REC

In the never-ending quest of the solar industry to improve photovoltaic (PV) technology and achieve the highest possible efficiency, researchers have tested many technologies, materials, and combinations. One option that outstands from the rest is the Passivated Emitter and Rear Contact (PERC) solar technology which allows for the creation of PERC solar panels.

The PERC solar panel is a highly efficient and improved type of PV technology that uses Crystalline Silicon (c-Si) and fixes some inconveniences of this traditional technology. In this article, we will do a deep and detailed analysis of what is a PERC solar panel, how it compares to older and other advanced technologies, as well as the different applications for PERC solar panels.

WhistlingBird, Silicon solar cell (PERC) front and back, Redesign, CC BY-SA 4.0

Recapping the structure and workings of traditional solar panels

Before diving into PERC solar panel technology and its benefits, it is important to have a proper understanding of traditional solar panels and how they work. Traditional solar panels are called monocrystalline and polycrystalline silicon solar panels, depending on their manufacturing materials. The basic structure of c-Si solar cells is comprised of the following layers:

• Printed silver paste (front contact of the cell)
• Anti-reflective coating or anti-reflective glass
• Doped semiconductor (P-N junction)
• Back Surface Field
• Print aluminum paste (rear contact of the cell)

The c-Si solar panels generate power by harvesting solar energy under the photovoltaic effect. The most important component to generate solar power is the doped semiconductor or P-N junction manufactured with an N-doped layer which is negatively charged with extra electrons, and a P-doped layer which is positively charged and therefore it has holes (missing electrons). The P-N junction works as the main structure generating solar energy in the cell.

On a simple basis, the load is connected to the solar cell and it is energized by the power generated from the cell, but it is important to understand the inner functioning of the solar cell. This will also help us understand more about PERC solar panels in the following sections.

When the P-N junction or photovoltaic material is hit with a photon, the electron within the semiconductor is excited. The electron is then moved to the conduction band, creating an electron-hole (e-h) pair.

Flow from the electron through the load - Source: The Physics of Solar Power from Colorado College

After the e-h pair is created, the electron usually goes to the front contact and the hole to the P-doped layer. During this process, the electron flows through the load, which creates the flow of electric current.

After the electron goes back to the solar cell through the rear contact, it recombines with a hole, ending the electrical current flow for that particular pair. This process is constantly ongoing whenever photons hit the surface of solar cells.

What are PERC solar panels?

While the recombination of the e-h pair under the aforementioned circumstances is the regular process generating an electric current for traditional solar cells, there is also another type of recombination called surface recombination, which produces losses for traditional crystalline silicon technology.

The surface recombination process occurs when a hole combines with an excited electron that did not go through the contact. This recombination process translates as a reduced solar cell efficiency since the e-h pair combines without generating an electric current or solar power.

On top of the surface recombination, traditional crystalline silicon solar panels can produce losses due to inefficiency in capturing light, reflection by the solar cell itself, and partial shading by materials in the module. To reduce efficiency losses, researchers in the solar industry developed the PERC solar cell.

PERC technology was first described in the University of New South Wales in but officially registered in a paper in . The PERC solar cell finally allowed PV modules to move over the 20% conversion efficiency that has been the norm for several years in the industry.

Structure of a PERC solar cell - Source: ENF Solar

The PERC solar cell technology includes dielectric surface passivation that reduces the electron surface recombination. At the same time, the PERC solar cell reduces the semiconductor-metal area of contact and increases the rear surface reflection by including a dielectrically displaced rear metal reflector. This allows photons to be absorbed when going into the cell or out of it, and it also reduces heat absorption.

This highly efficient and improved version of c-Si technology results in PERC solar panels having a 0.86% or more increment in the efficiency of the solar cell. This provides several perks like a reduced installation time, fewer space requirements, and cost reductions by requiring fewer wires, connectors, racks, and other components that you would require when installing the same PV capacity with traditional technology.

Mono PERC vs. Poly PERC solar panels

Since PERC is a technology implemented on traditional crystalline silicon solar cells, PV modules under this technology are divided between mono PERC solar panels and poly PERC solar panels.

Poly PERC solar cells are manufactured by blending or melting different silicon fragments together, while mono PERC solar cells are manufactured using a single silicon crystal, free from grain limits (2D defects). Since mono PERC solar cells have a higher level of purity, these PV modules are more efficient, but they are also slightly more expensive.

Studies performed in  provide us with enough data to have a deeper understanding of PERC technologies and how they compare to traditional panels.

Poly c-Si solar cells with 18.46% efficiency get an increased efficiency of 18.61% when manufactured with PERC technology, the difference is even more notorious with mono c-Si solar cells. A traditional mono c-Si panel has a 19.55% efficiency, but this efficiency increases by 0.86% to achieve 20.41% for mono PERC solar panels.

Mono PERC solar panels tend to have a relatively higher price, but considering the performance and technical specifications against the price, this technology is much better than poly PERC solar panels.

PERC solar panels vs. Other advanced panel technologies

PERC is only one of the available technologies to improve efficiency and applications for solar panels. There are other advanced technologies like Interdigitated Back Contact (IBC) and Bifacial Solar Cell (BSC) technology. Manufacturers can use either one or even combine PERC with IBC or BSC. In this section, we compare IBC and BSC against PERC technology, to fully understand the perks of this technology.

PERC panels vs. IBC solar panels

One interesting improvement performed to solar cells is the implementation of Interdigitated Back Contact technology. Most cells (PERC included) have a thin strip of conductors in the front, which are called busbars, these conductors are used to transport the electric current through the cells.

While the space occupied by the busbars is not that large, it is still a surface area of the solar cell that could receive photons to generate solar power. To reduce losses, IBC solar cells place the conductors on the back of the cell, leaving the frontal surface entirely exposed to the sun, allowing the whole IBC solar cell to receive photon impacts and generate solar power.

Efficiency for IBC solar cells is higher in general, but the highest recorded efficiency for both technologies is similar. The highest efficiency for PERC solar cells was recorded at 25.0%, while IBC solar cells achieved a 25.4% conversion efficiency.

The biggest downside for IBC technology is that it has a higher cost than PERC solar panels. An advantage is that manufacturers can combine both technologies and obtain an even higher-performing PV module.

PERC panels vs. Bifacial solar panels

One of the most underused resources in solar applications is albedo. This is the diffuse solar radiation reflected from surfaces onto the PV module. To fully take advantage of this solar resource, manufacturers implement reflective rear sides or dual-panel glass, creating bifacial PV modules.

Bifacial technology can absorb direct light coming from the sun (like PERC solar panels), but it can also generate power from albedo light being reflected on the rear side of the module. Bifacial c-Si PV modules can deliver a higher performance ratio (PR) for the PV system, delivering 6% more PR than monocrystalline silicon modules, while PERC modules can deliver around 1% more efficiency than traditional technologies.

The good news for the solar industry, is that bifacial and PERC technologies can be combined, to create bifacial PERC PV cells. These new and innovative solar cells can deliver up to 18% more power than monofacial solar cells.

Key takeaways: Pros and cons of PERC panels

Understanding how PERC solar panel technology works, is key to understanding the pros and cons of different applications. In this section, we round up the major pros and cons of PERC solar panel technology and highlight some of its best features.

Pros

• Up to 1% more efficiency than traditional c-Si solar panels.
• Reduced heating absorption, allowing PV systems to perform better at high temperatures.
• Operation on a wider light spectrum.
• Better usage of the available space.
• Cost-effective technology.
• Prices for PERC solar panels will get reduced as the technology becomes more popular.
• PERC solar cells can be combined with IBC or Bifacial technology.

Cons

• Relatively larger cost than traditional technologies.
• Light-Induced Degradation (LID) and Potential-Induced Degradation (PID) were a problem in the past for the technology. (Not anymore, since most manufacturers overcame these barriers).

Final Thoughts

Passivated Emitter and Rear Contact (PERC) technology is an excellent improvement that allows solar cells to achieve higher efficiencies. While this technology presented several cons in the past like LID and PID, manufacturers found ways to solve this, resulting in high-efficiency PERC solar panels without the cons of the technology in the 80s.

Since manufacturers can either design regular PERC solar panels or combine them with IBC or bifacial technology, the range of applications for this technology is quite broad. PERC solar panel technology can be used on residential, commercial, and industrial applications (including utility-scale applications).

For residential purposes, PERC solar panels can be used as regular rooftop photovoltaics, EV solar roof chargers, and solar sheds. For commercial and industrial applications, this technology can be used for ground photovoltaic power stations (especially when combined with bifacial technology), Building Integrated Photovoltaics (BIPV), water surface power stations, and much more.

The use of this technology is quite convenient for the solar industry in general. With the rise of PERC solar panels, homeowners and utilities can benefit by using less space, fewer installation components, and using PV modules with higher performance and an infinity of applications.

If you want to learn more, please visit our website PERC PV Module.