Yash
Interdigitated Back Contact (IBC) is one of the most advanced solar cell technologies that improves efficiency.
The IBC cell technology captures more energy than conventional (Al-BSF: Aluminum-backed surface) solar cells, by minimizing the shading and increasing the light absorption rate.
Hence, improving the cell’s efficiency. The rear side of the cell reduces the recombination losses by strategically separating the hole and the electrons through interdigitation.
What is interdigitation?
Let us learn about it through its manufacturing and working.
The structure and the working of IBC solar cell
The N-type crystalline silicon is the main layer which acts as an absorber layer.
This layer is formed when the thick silicon wafer is doped with a pentavalent impurity such as Phosphorus.
Thereafter, a very thin layer of P-type doped wafer (when silicon is doped with a trivalent impurity such as Boron) is placed over it to create an N-type solar cell.
Then crystalline silicon is pasted with a passivation layer made of Al₂O₃ (confirm) on both sides.
Thereafter, the antireflection coating of Silicon Nitride is pasted on the front and the rear surface of the cell.
Now, comes the major structural modification which makes it different and more efficient than the conventional solar cells.
It is the inclusion of the diffusion layer at the back of the cell which features interlocked layers (interdigitated) of n-type and p-type layers over it, creating the base for the metal contacts over it.
(It looks like the fingers of one hand are locked with the other).
Finally, the metal contacts are fused over this diffusion layer, freeing the front side from the shading material.
The working of IBC solar cell
The IBC solar cells work just like any other conventional solar cell.
The electrons of the cell get excited upon absorbing the photons of light and move to the conduction band.
Now, these electrons are free to move and collected at the rear of the cell. When the load is connected to the cell, these collected electrons are channelized into the load, and we get electricity.
Benefits of IBC solar panels
1. Aesthetically appealing
As they do not have any visible contacts on the front side, they look more appealing to the eyes.
Moreover, this technology can be seamlessly fitted into developing or under-construction projects giving house roofs a more aesthetic sense and an affordable solar option for the buyer.
2. No hotspots
Do you know that the uneven distribution of the sunlight over the solar cells can overheat them?
When some cells of the solar panel receive less light than the surrounding cells due to the shade over them, those cells start operating in the reverse bias.
Thereafter, the current starts flowing inside them. This raises the cell temperature and starts overheating it, reducing its efficiency and permanently damaging it. This process is called hotspots.
We have a solution…
The highly efficient IBC solar panels have lower sensitivities towards the temperature variation in the solar cells. Hence, they maintain a uniform current flow even when the solar cells in the solar panel are shaded.
Thus, minimizing the possibility of cell damage due to the hotspots.
Tip: Keep an adequate gap between the adjacent solar panels and the ground for air ventilation. Also, clean your solar panels regularly.
3. Reduced series resistance
The metal contacts on the rear side are given a larger surface area. This reduces their resistance.
(As the surface area increases, the resistance decreases. The resistance is inversely proportional to the surface area of the material.
It can be written as Resistance α length/Area)
When these solar cells with larger metal contacts are connected, they make a solar panel with the least series resistance.
4. High weather resistance
As the contacts are relocated at the back of the solar cells. It protects them from direct degradation of weather’s harsh conditions such as moisture and heat. Hence, reducing their degradation with time than the solar panels which have the contacts in their front side.
As these solar cells have a larger surface area, they get cooled faster than conventional solar cells having frontal contact.
5. Lower temperature coefficient of power
It is a fact that the output of the solar panel decreases with the rise in its cell temperature beyond 25ᵒC.
Every solar panel whether it is n-type or p-type, monocrystalline or polycrystalline loses some power with the rise in its cell temperature.
The temperature coefficient of power tells us how much power a solar panel is going to lose.
It is measured in %/ᵒC.
The lower the value, the better it is.
The IBC solar panels have a lower temperature coefficient of power than the PERC solar panels and other conventional solar panels.
You will find that conventional solar panels have an average value of -0.35%/ᵒC.
While the IBC technology solar panels have it -0.29%/ᵒC.
Let me explain you about this:
The formula for finding the power loss with the rise in the temperature is:
Power loss (%) = (cell temperature – 25ᵒC) * temperature coefficient of power
Assuming the cell temperature of 65ᵒC
Putting the values in the above formula, we get
Power loss in IBC solar panel = (65ᵒC -25ᵒC) *-0.29%/ᵒC
= (40 ᵒC) * -0.29%/ᵒC
= -11.6% (The negative sign indicates the power loss)
Assuming I have a 500-watt solar panel, it will lose 11.6% at 65ᵒC that is 500 watts x 11.6% = 58 watts.
You will get 500 watts – 58 watts = 442 watts
While conventional solar panels the power loss at the same cell temperature would be 14%.
(The average power loss in conventional solar panel = (65ᵒC -25ᵒC) *-0.35%/ᵒC
= (40 ᵒC) * -0.35%/ᵒC
= -14% (The negative sign indicates the power loss)
Assuming I have a 500-watt solar panel, it will lose 14% at 65ᵒC which is 500 watts x 14% = 70 watts).
One thing I can say for sure is that the IBC solar panels are the best option for hot climates.
6. Long warranty
- The output of the solar panel decreases with time. The performance warranty assures that even after 25 years or 30 years the output of the solar panel will remain a certain percentage of P(max).
The IBC solar panel degrades < 1% of Pmax in the first year.
While the other solar panels deteriorate by 2% to 3% in their first year.
Thanks to its N-type silicon substrate.
The N-type cell is more immune to Light-induced degradation than the P-type solar cell.
In the P-type solar cell, the bulk silicon wafer is doped with trivalent impurities such as Boron. When the p-type solar is exposed to the sunlight, it makes Boron-oxygen complexes in the presence of the sunlight.
These complexes hinder the electrons in making the photovoltaic effect.
On the other hand, in the N-type solar cells, they are doped with pentavalent impurity (Phosphorus). Hence, they do not make these complexes and let the free electrons participate in the photovoltaic effect. From the 2nd to the 25th year, the degradation is 0.25% per year till the 25th year.
This makes the solar panel output close to 93% of its P(max) in the 25th year.
Which is great…
7. The IBC solar panels are highly efficient
Both technologies IBC and PERC have higher efficiencies, lower temperature coefficient of power, and long warranties.
The PERC technology reduces the surface area of the busbars and the metal contacts in the front of the cell.
The IBC technology goes one step further and it even eliminates the area occupied by the contacts by relocating them to the rear side of the cell.
In this way, the cell has a larger photon absorption area and this increases the efficiency of the IBC solar cell more than the PERC solar cell.
Till now, the maximum efficiency achieved through PERC solar cells is 25.4% while the IBC solar cells have the maximum efficiency of 26.7%.
Their high-efficiency value makes them the best candidate for places with low light conditions.
Drawbacks of IBC solar cell
The main drawback of this technology is that it is complicated to fabricate, relocate, and isolate the interdigitated n- and p-type contacts on the rear side of the cell.
The second complication with this technology is the rear passivation contact film optimization.
It is due to the presence of dual impurities at the rear end of the cell, the single dielectric passivation layer needs to be optimized to pacify the heavily doped p-type and n-type dopants.
The solution could be:
- Using a passivating layer with low interface defect density
- Eliminating the undiffused areas at the rear side of the cell such that the heavily diffused n-type and p-type regions are adjacent to each other.
Top manufacturers of IBC solar panels
- Aiko Black hole series (China)
- FuturaSun FU 360 M Zebra (Italy)
- LONGi Solar Hi-MO 6 Scientist (China)
- SunPower Maxeon® solar panels (USA)
Concluding statement
The IBC technology solar panels are the next-generation solar panels with the highest efficiencies.
They are used in residential and commercial applications.
Their lower temperature coefficient of power makes them the best option for people living in a hot type of climate.
They are immune to the LID effect, no hotspot problems.
The main drawback is the complicated fabrication technique which increases their cost than their counterparts.
However, with time it would be interesting to see this technology evolving and capturing more market share in the solar industry.
To be continued…
