The HJT solar cell was first introduced in the early 1980s by Sanyo and later by Panasonic of Japan. The product cost of the HJT solar cells has reduced significantly in the last decade.
This technology is becoming one of the top choices of manufacturers for making solar panels with increased efficiencies.
What is Heterojunction solar cell?
The HJT solar cell is made by sandwiching the N-type crystalline silicon between the thin layers of amorphous silicon.
Hence, it uses both crystalline and thin-film technology.
The thin films of amorphous-silicon ( ̴120 micro-meter) are pasted on both sides of n-type crystalline silicon, HJT solar cell is made.
The thin-film amorphous silicon and crystalline silicon work complementary.
On one hand, crystalline silicon absorbs most of the sunlight while on another hand, a-silicon prevents electron-hole re-combination due to its passivation property.
This dual effect increases the harvesting power of the HJT cell that you do not find in a traditional solar cell.
Benefits of Heterojunction solar panels
1) N-type HJT cells are more immune to the LID effect.
The light-induced degradation is the loss in the panel output within the first few hours of its exposure to the sunlight.
The LID effect is prominent in P-type (boron-doped) solar cells. During its manufacturing, the oxygen atoms get trapped in the cells.
When they are exposed to the sunlight, the oxygen reacts with the boron to form a complex boron-oxygen compound.
This complex compound makes it free electrons difficult to produce a photovoltaic effect.
Thereby you see power loss in the solar panels based on p-type (boron-doped) solar cells.
There is no such compound formed in the HJT solar cells when exposed to sunlight.
Therefore, they are more immune to the LID effect.
You see less degradation in the solar panels based on this technology.
2) The HJT cells are encapsulated in a highly resistant polymer back-sheet and are laminated in anti-reflective glass.
This makes it difficult for water and humid air to penetrate the cells. Therefore, they can be used in hot and humid climates.
Read: Best solar panels for hot climate
3) They have a lower temperature coefficient of power: when the electron leaves its excited state drops into the hole, it is called recombination.In this process, energy is released.
It can be in the form of heat.
The ultra-thin amorphous silicon layer is very effective in preventing electron-hole recombination.
This passivated property checks the heat generation, making HJT cells having a low-temperature coefficient of power.
Please see the part of the datasheet of REC Alpha series solar panels.
They are based on HJT cell technology
We see that they have -0.26%/°C as the temperature coefficient of power.
This value is one of the lowest in the market.
Assuming, the solar cells are operating at 45 °C, the power loss would be:
Power loss (%) = (cell temperature - 25 °C) x temperature coefficient of power
= (45 °C – 25 °C) x -0.26%/°C
= 5.2% of power is lost at 45 °C
It means that they can be used effectively in hot climates.
4) They are bi-facial by nature, as thin films of a-silicon are pasted on both sides, they can produce current from the rear side as well, leading to about 15-20% more energy than the traditional mono-facial solar panels.
It means, you need fewer panels to meet your energy needs and less space is required.
Top HJT solar panel companies
If you already have a PERC module plant, shifting to the HJT technology based would be financially unattractive.
When you are starting from scratch, setting up an HJT plant is profitable as they are efficient than the other traditional panels.
I am expecting many more manufacturers would be coming up with new HJT production lines.
As a homeowner, if the benefits of HJT solar panels outweigh the cost involved.
It is a good option to go for the solar power system on the roof.
Why not try Solar Feasibility Spreadsheet to know the return from your solar power system?
It designs the complete solar power system and finds the financial feasibility beforehand.
In that way, you make an informed solar decision.