PERC Cell Technology: [All To Know About]
Solar PV systems have energy losses at different stages of converting solar energy to electricity.
These losses are associated with solar panels, inverters, cabling, and other electrical equipment that are used to build these systems.
Scientists and solar PV systems manufacturers are constantly trying to reduce these energy losses and improve the overall efficiency of solar panels.
We know a solar PV system is only as efficient as the cells that make it up. When a solar module or collection of modules is made from less efficient cells, the result is a PV system that often fails to meet its expectations.
Therefore, using better solar cells with higher conversion efficiencies is the first and most important step in reducing the losses of a solar PV system.
The standard aluminum back surface field (Al-BSF) design has accounted for over 90% of global solar cell production for decades.
This cell design is widely accepted as a cost-effective solution due to its extensive knowledge of manufacturing tools, materials, and methods.
However, cell technology has advanced significantly over the years, and efficiencies have increased.
A relatively newer cell design, PERC (Passivated Emitter and Rear Cell) has emerged as a better alternative to the conventional BSF design.
Although PERC technology has been known since 1989, commercial implementations have run into issues due to growing light-induced degradation.
PERC modules, as a result of continuous enhancements over time, are more efficient than standard solar cells by about 1%.
This number may seem not much. But in reality, this is a huge improvement since a small improvement in efficiency can lead to a large increase in overall energy production.
Considering that a traditional standard module typically has a 20% efficiency, a system utilizing PERC modules will produce about 5% more energy than a system using traditional modules provided all else is kept equal.
The passivated emitter and rear cell (PERC) design have a current and prospective commercial cell efficiency of 21–24% while requiring only minor modifications to typical Al-BSF processing.
This offers for the continued use of existing industrial equipment, materials, and processes.
The two main advantages of PERC’s over the Al-BSF cell: reduced rear-surface recombination and improved rear-surface reflectivity that we are going to mention further in this post.
What Is PERC cell?
PERC (Passivated Emitter Rear Cell) technology is a solar cell manufacturing technique that increases the efficiency of silicon wafers by adding an anti-reflective coating on the rear side.
Because of this extra layer, more sunlight can be captured and converted into power, making PERC cells more efficient than traditional cells.
PERC modules can also reduce rear recombination and keep longer wavelengths from producing heat, which would otherwise degrade the cell’s performance.
How does PERC increase energy efficiency?
PERC technology improves the overall performance of a cell by boosting a cell’s light-capturing ability.
A typical solar cell is composed of two layers of silicon with distinct electrical properties: the base and the emitter.
When negatively charged particles (electrons) come into contact with the interface, a powerful electric field is generated, which draws them into the emitter.
Light entering the cell and releasing electrons from the silicon atoms generates the electrons. Electrons flow freely through the cell and contribute to the electrical current only if they reach the interface.
Different wavelengths of light generate electrons at different levels of the cell structure.
Shorter wavelengths (blue light) generate more electrons near the front of the cell, while longer wavelengths (red light) generate electrons at the back of the cell or even pass through the wafer without generating current.
The addition of PERC technology increases cell efficiency by reflecting back into the cell any light that has passed through to the rear without producing electrons.
As a result of this reflection, photons are effectively given a second chance to generate electricity.
The ability to capture longer wavelengths of light, such as when the sun is at an angle (early mornings and nights) or when it is cloudy, increases the energy yield of PERC cells.
When the Sun is directly overhead, a greater amount of blue light (wavelengths between 450 and 495 nm) is absorbed by the atmosphere because it has a longer path to the Earth’s surface.
Blue light is generally converted to energy near the top of the cell, whereas red light (wavelengths 620 to 750 nm) penetrates deeper and is converted to energy near the bottom.
Because the Earth’s atmosphere absorbs red light easier, cells that collect more red light are often more potent.
The PERC technology’s reflecting properties boost red light absorption even in low or diffuse light conditions, increasing energy yields.
The silicon wafer does not absorb wavelengths over 1180 nm. These wavelengths are simply absorbed into the backside metallization of standard cells, raising the cell temperature and decreasing conversion efficiency.
Because the PERC layer reflects this light back through the cell and out of the panel, the amount of absorption by the aluminum metallization layer, and thus heat buildup within the cell, is reduced.
Because of the reduced absorption, the cell can operate at a lower temperature, increasing the energy yield.
What are the advantages of PERC technology?
PERC modules have several advantages over traditional solar cells:
Higher conversion efficiency
PERC cells offer a higher conversion efficiency compared to traditional solar cells due to the anti-reflective coating on the rear side.
Reduced rear recombination
A PERC module will reduce the amount of current loss due to electrical recombination in the rear side of the cell.
PERC cells will have a longer lifespan than traditional solar cells because they will produce less heat.
What are the disadvantages of PERC technology?
However, there are also some disadvantages of PERC technology:
LID (Light Induced Degradation)
LID is a kind of solar cell degradation caused by sunlight which is enhanced by the anti-reflective coating of PERC cells.
It can be prevented through careful design and material selection, but it is still a problem with this technology.
PID (Potential Induced Degradation)
PID (Potential Induced Degradation) is another kind of solar cell degradation that changes the module’s potential in relation to the ground and reduces the module’s power over time.
The primary source of PID is an abnormally high voltage between the encapsulated solar cells and the front glass surface, which is grounded through the frame or structure.
This can cause unintended migration of charge carriers (ions/electrons), lowering the cell’s performance.
The PID effect can be more pronounced when high voltages are present due to lengthy string connections. Also, the PID process is accelerated when there is high humidity and temperature in the environment.
Because PID usually appears months after the PV system is installed, it is a serious problem that can significantly reduce the system’s overall performance without warning.
Furthermore, unlike other module flaws (such as delamination or EVA component yellowing), the PID cannot be seen with the naked eye.
The best thing to avoid PID is selecting solar modules that have been certified for PID resistance in accordance with IEC TS 62804.