A solar cell is a device that converts the energy of light into electrical energy. It is called the photovoltaic effect. Solar cells are commonly arranged in arrays to form solar panels. They are the main component of the PV modules: their value is around 70% of the total product.
Figure 1 – Solar cell in production (source: PV Magazine）
Silicon is the most common material used to manufacture solar cells: 90% of the PV cells sold in the world are made from this material. Firstly, it is the Earth’s second-most abundant substance (after oxygen). Also, silicon-based solar cells have high efficiency combined with cheap costs and a long lifetime.
The ratio of electricity generated by the solar cell to the energy it received is called cell efficiency. It shows how well the cell converts light energy to electrical power. The quality of the light and attributes of the cells will impact this ratio.
What are the main cell technologies?
Passivated Emitter and Rear Contact – PERC
At the origin, PERC technology came from the modification of conventional solar cells. An additional layer was added to the traditional solar cells to allow them to capture more sunlight, thus producing more energy.
It is the main technology used in the market. Its low price and flexibility in larger wafers have enabled large-scale production capacity expansion for PERC cells. It still benefits from a solid supply chain and a large quantity of compatible production equipment.
But the efficiency of PERC cells has reached its limits. After a yearly improvement of 0.5% these last years, it has now slowed down. To reach new efficiency levels, the market will have to look to new technologies.
Passivated contacts (TOPCon)
TOPCon technology was first introduced in 2013 but has been used by manufacturers since 2019. To have a TOPCon cell, a tunnel oxide layer is combined with PERC solar cells. This means PERC cells and modules equipment can be easily adapted to the production of TOPCon cells and modules.
They benefit from a higher efficiency and higher bifaciality rate than PERC cells.
Heterojunction (HJT)
Heterojunction technology combines the advantages of thin-film absorption and passivation properties of amorphous silicon. Two thin layers of amorphous silicon are applied to both sides of an n-type silicon wafer to create the HJT cells.
Heterojunction technology still holds the silicon solar cell efficiency record at 26.63%, thanks to a combination of HJT and IBC. Moreover, they have a lower temperature coefficient and the highest bifaciality rate of all types of cells.
Heterojunction cells need fewer production steps than PERC and TOPCon but they require all new lines, which requires a high capital cost. They also have a higher usage of silver. New alternatives are still in the research phase.
Tandem cells (3rd generation PV cells)
All the previous technologies will reach their practical efficiency limits in a short period of time. This is why the industry is already working on the next generation of cells, which will be manufactured with several materials to produce energy from a larger light spectrum.
C-Si/Perovskite tandem cell is the most promising technology. The potential efficiency could go beyond 35%.
