PERC Solar Cells: What Are They & How Do They Work? [2022 Guide]
In this solar guide, you’ll learn:
- What PERC cells are and how they differ from standard ones
- How PERC cells work to improve panel efficiency
- What the best PERC panels in the industry are
What Are PERC Solar Cells?
PERC — Passivated Emitter and Rear Contact or Passivated Emitter and Rear Cell — solar cells are a relatively new solar technology that was first developed in 1989. The new design sought to solve some of the hard efficiency limitations that traditional cells presented.
Traditional cells saw jumps in efficiency when panel manufacturers began putting a front passivation layer to prevent electron recombination at the front panel. Additional bumps in efficiency were achievable by reducing the number of electrons that hit the rear of the panel.
PERC cells take this one step further by placing an additional capping and passivation layer on the rear surface of the photovoltaic (PV) panels, thereby reducing back-side recombination. These layers also help prevent the panels from heating up from unreflected solar radiation. Since panels perform better in cooler temperatures, this helps boost performance as well.
Blue Raven Solar
Types of PERC Solar Cells
There are two primary types of PERC solar cells, which are subcategories that also apply to traditional cells: monocrystalline and polycrystalline.
- Monocrystalline PERC cells — mono PERC cells — are made from a single piece of silicon. Mono cells are more efficient primarily because they lack the seams between silicon crystals that can sometimes scatter light.
- Polycrystalline PERC cells — poly PERC cells — are manufactured using much smaller silicon shards. The manufacturing process is much more affordable, so poly cells are cheaper. However, the light-scattering effect they can cause reduces conversion efficiency.
- Traditional solar modules can also be made as thin-film panels, which are the most affordable but the least efficient. PERC cells are currently not available in thin-film applications.
PERC Solar Cells Vs. Traditional Solar Cells
There are only a few key differences between PERC and traditional silicon solar cells. However, these differences lead to significant variances in overall efficiency and panel production and installation costs. Some of the primary differences are listed below.
- PERC cells are more efficient because they avoid rear-side electron recombination and increased panel temperature from solar heat
- PERC cells have a maximum efficiency of around 23%, while traditional cells max out at around 20%
- Both types of cell use two layers of silicon, often called the n-layer for negative and p-layer for positive. Electrons traveling between these is what leads to solar energy production
- Installations for PERC cell panels are often cheaper because the higher efficiency means fewer panels are required to meet the energy needs of the user
- PERC cells have more boron in the materials, so the risk of Light-Induced Degradation (LID) is heightened. However, manufacturers have implemented ways to reduce the risk of this loss of efficiency
- PERC technology can be added to traditional cells. That means that PERC cells will naturally be a bit more expensive
- PERC cells are bifacial, meaning they can produce energy coming in from both sides of the panels. Standard solar cells are not bifacial and can only utilize solar energy coming in from the top face
- Traditional cells have the larger market share, and the new technology is currently lagging behind
How Do PERC Solar Cells Work?
To understand how PERC cells work, it’s important first to understand how traditional cells work.
How Traditional Cells Function
Traditional cells consist of a front contact on the face of the panel that receives sunlight, the n-type silicon layer below that, followed by the p-type silicon layer and the rear contact. As sunlight passes through the front contact, valence electrons in molecules located in the silicon layers are ejected toward the back of the panel, where they are harnessed for energy.
When the electrons are discharged, an imbalance in the positive and negative silicon layers causes a rebalancing of positively charged “holes” — a lack of a valence electron — and the negatively charged molecules with an additional electron. Continued solar energy entering the cell recreates this process over and over, and electricity continues to flow from the panel.
How PERC Cells Work Differently
PERC cells work in a similar manner but with a few key differences.
The n-type sheet, which is negatively charged, typically contains more atoms that have an additional electron in their outer shell — like phosphorus — to maintain that negative charge.
The positive p-type sheet contains positively charged holes into which those additional electrons can fit. These are usually boron or gallium, which lack one valence electron needed to bond with the silicon around it.
The atoms missing an outer electron — the holes — naturally bond with the atoms that have an extra valence electron. This leaves one additional electron out of the bond, which then gets discharged and collected as electricity.
When solar energy enters the panel, the positive and negative silicon layers naturally rebalance, and the process begins again. While the underlying idea is the same, PERC cells have a few additional layers to prevent the loss of electrons to the outside world.
What The Additional Layers in PERC Cells Do
First, they have a dielectric capping layer to prevent the reflection of unused solar energy and an increase in inner-panel temperature. This single layer helps increase the amount of sunlight that enters the PV module and is usable for continuing the imbalancing-balancing process described above.
Additionally, this layer helps prevent recombination. Recombination is when electrons drop from the conduction band — the electron band under the valence band — to the valence band.
The issue with surface recombination is that electrons that could otherwise bond to holes in the silicon cell are left without the potential for bonding around the edge of the cell. The capping layer provides a means of using these dangling bonds to push solar energy production rather than remaining unused.
PERC cells also contain a passivation layer, which prevents electrons and holes from recombining at inopportune times and at inopportune places in the silicon layers. Electrons and holes that combine near the surface can result in a loss of energy, as the emitted electron may not be collected for conversion to AC electricity by the inverter.
As you can probably imagine, the ideal situation is for all of the additional electrons and holes within a cell to combine where and when the extra electron can be collected and used for energy production.
Both the capping layer and the passivation layer are slightly reflective as well. This means some of the solar energy entering the top of the cell that would otherwise escape through the back is reflected back into the silicon layers to be utilized by the cell.
This not only boosts efficiency but also prevents some of the longer wavelengths from increasing the inner temperature of the cell by becoming heat. An alternative in traditional cells is to add a back surface field (BSF), but this isn’t as efficiency-boosting as the PERC solar cell technology.
What Are the Best PERC Solar Panels?
Since they were invented, PERC panels have become significantly more efficient and, as a result, more prevalent in the renewable energy industry. Several of the top panel manufacturers now offer PERC panels as a part of their standard product lines.
The table below includes some of the best PERC panel options, along with some panel specs to help you decide if one of these panel brands is right for your solar project.
|Model||SunPower/Maxeon P-Series||Jinko Solar Mono PERC 78 Cell||Q Cells Q.ANTUM||REC TwinPeak 2|
|Efficiency Rating (Max)||20.4%||20.58%||19.5%||17%|
|Watts||370 to 390||425 to 445||480||300 to 330|
|# of Cells||498 (overlapping strips)||78||78||120|
What Are Other Efficient Solar Panel Options?
PERC cells have been around since 1989, and they’ve gone through a lot of changes since they were introduced to the solar industry. There are a handful of other solar cell options available that have been developed alongside PERCs to boost solar cell efficiency. We’ll discuss some of these options briefly below.
Tunnel Oxide Passivated Contact (TOPCon) Cells
TOPCon cells have two important additions that PERC cells don’t: a layer of phosphorus-doped silicon and a thin layer of silicon dioxide. TOPCon cells are often looked at as the next step above PERC cells, as they seek to solve all of the same issues but further reduce minority carrier recombination.
Minority carrier recombination can either lead to a loss of potential solar power or an increase in the long wavelengths that become heat. Higher temperatures make your panels less efficient, so limiting recombination is always a positive thing.
The TOPCon technology can be added to traditional or PERC cells, so it remains a great option for boosting solar panel efficiency. However, it will drive up the cost of the panels a bit.
Heterojunction (HJT) Cells
Heterojunction (HJT) cells are currently the most efficient option available, with the hard efficiency limit hovering around 26.7%. However, unlike PERC and TOPCon technology, HJT technology cannot simply be added to traditional cells. As such, they are significantly more expensive than the other types of cells.
HJT cells consist of crystalline silicon wafers interspersed with amorphous silicon layers. In an alternating pattern, these cells minimize surface recombination as much as s possible with current technology. The result is fewer wavelengths becoming heat and more solar energy being able to be used for solar power generation.
HJT cells could become more common if the solar industry as a whole begins to shift toward producing these. The manufacturing process is currently set up to produce traditional cells, and adding the capability to include PERC and TOPCon solar technology is not terribly expensive or complicated.
Making HJT cells commonplace would require a revamping of the entire manufacturing process. This would be extremely expensive and time-consuming, which is likely the reason these higher-efficiency cells haven’t become the norm yet.
Perovskite cells contain silicon layers with a different crystalline structure, which is similar to that of the natural compound, perovskite.
When originally developed, these high-efficiency layers contained lead, which is highly toxic to humans and the environment. Researchers have since started to use tin as an alternative, although the tin-based cells degrade much more rapidly.
Despite the toxicity, perovskite PV cells have a theoretical maximum efficiency of around 38%, which is a massive improvement — nearly twice the efficiency — over all other types of PV cells. The actual performance of these cells has reached around 30% to set the world record for efficiency. This makes them particularly good in low-light conditions.
As mentioned above, perovskite cells made using tin degrade quickly, which means the lifespan of panels would be significantly reduced. This makes real-world applications a challenge, although developers are confident that the efficiency will make production worthwhile.
Similar to HJT cells, perovskite cells are produced in an entirely different way than traditional, PERC and TOPCon cells. Mass production of this style would require a reworking of the manufacturing process, which would be expensive.
These cells are set to hit the market in 2022, but wide availability will not be possible until they can be mass-produced. For that to happen, real-world efficiency will likely need to continue to increase toward the theoretical maximum, and production costs will need to come down.