There are many technologies today for manufacturing and structuring the silicon solar cell.
For example, the traditional silicon solar cell, also known as Al-BSF (Aluminum Back Surface Field), is composed of a two-sided silicon layer with a single P-N junction, doped with phosphorus and boron.
You might also have heard of the passive emitter rear contact (PERC) cell technology that addresses transmission losses through the introduction of a dielectric layer.
And finally, there’s a HIT or a heterojunction with an intrinsic thin layer solar cell technology, that focuses on the reduction of recombination losses by adding amorphous layers.
However, in the structuring of solar cells, there are many paths to harness electricity from sunlight. Some are more difficult to manufacture than others, but sometimes they offer tremendous advantages.
That is the case of IBC cells. Let’s take a look at this technology!
How Do IBC Cells Work?
Interdigitated Back Contact (IBC) cells may be one of the most complicated technologies used to fabricate solar panels, but it also offers efficiency values that cannot be ignored, which is why it is considered an important alternative today.
Traditional solar cells achieve energy conversion by placing front contacts in the cell. This means photons that reach the surface of the cell must be absorbed at that moment to release electrons and produce electricity.
If they are not absorbed they are transmitted or reflected. This can be considered a loss.
IBC cells implement a different idea. Instead of placing the contacts in the front of the cell, they place them on its rear side.
This allows them to achieve higher efficiency due to reduced shading on the front of the cell, while at the same time electron-hole pairs generated by the absorbed light can still be collected on the rear side of the cell.
On the illustration below you can take a look at the structure of IBC cells, from a rear side point of view.
The Benefits of IBC Cells Compared to Al-BSF
Lower Shading Losses
First and most important is that the shading loss caused by the front side electrode (contact) is nil, which allows gains between 5-7% to be achieved in the generated current.
Lower Series Resistance
Moreover, as you can see in the illustration above, the contacts on the rear side occupy a larger area.
This is associated with a much lower series resistance due to the fact that the space between the contacts is insignificant when compared to a conventional solar cell.
It is only possible to do this with rear side contact cells as there is no need to leave a wider space opened in the front side for light absorption.
This is a really interesting feature when considering concentrated PV (CPV) cells where the effect of series resistance is hugely important.
Independence Between Optical and Electrical Optimisation
There is a great advantage in decoupling the optical optimisation from the electrical optimisation.
In traditional solar cells, there has to be a limited trade between the series resistance, the recombination losses, the absorption of light, efficiency and high open circuit voltages, as both the electrical conduction and energy conversion are performed in the front side.
In IBC cells, the two functions are independent of each other. The optical optimisation is performed on the front side, while the electrical optimisation is performed on the back side.
Why IBC Cells Are More Complicated:
- The current flow of carriers is done in two-dimensions, while on standard cells it is only one dimension.
- The efficiency of the IBC cell is deeply related to the BSF lifetime and the front surface recombination, demanding higher quality silicon wafers with a longer carrier lifetime.
- Alignment of n-type and p-type regions on the same side of the wafer (rear side) is more complicated.
- Sophisticated cleaning procedures and superior contamination control is necessary for the manufacturing process.
The IBC solar cell is an innovative technology that presents a different approach for both manufacturing and harnessing electricity from sunlight.
There are major benefits that can be obtained by placing the contacts on the rear side of the module.
One of the most important is the efficiency that can be achieved. For example, on Trina Solar’s IBC solar cells efficiency of up to 25.04% was achieved in February 2018.
Based on these advantages, the IBC technology was widely used until 2003 for CPV applications as the silicon solar cells could be used in several hundred times the amount of concentrated sunlight.
Then, in 2004 SunPower Corporation released the first IBC module and the technology started to be applied on regular solar installations.
The market share of this technology is expected to be around 35% (shared with HIT cells) by 2025.
Nevertheless, IBC cells are still highly valued today in applications where higher current values are needed like for CPV, solar race cars and even solar aeroplanes.
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Photo credit: Trina Solar