TOPCon technology boosts solar module and cell efficiency significantly

The below articles elaborate on how TOPCon improves passivation at the contacts, facilitating the transfer of the light-generated electrons from the silicon cell to the metallic contact with minimum losses.

Significant features of TOPcon technology

Solar cells are made from silicon wafers. To generate a voltage from sunlight (hence the name “photovoltaic”), the silicon wafer is doped with chemicals. Doping the silicon wafer with boron creates P-type silicon while doping with phosphorus creates N-type silicon. When the N-type and P-type silicon come into contact, a junction is formed (known as the P-N junction). This junction generates an electric field in the material and helps develop the voltage across the solar cell. An N-type solar cell means that the silicon wafer was initially N-type (phosphorus-doped), on which some boron was diffused on the top side to create the P-N junction. Unlike P-type cells, which experience degradation in sunlight due to the formation of boron-oxygen complexes (a phenomenon called LID), N-type cells do not degrade since the bulk silicon is boron-free.

TOPCon solar cells are generally made from N-type cells by adding additional layers to the cell. These additional layers (consisting of SiO2 and phosphorus-doped polysilicon) are added to the rear side of the solar cell before incorporating the metallic contacts. Their role is to improve passivation at the contacts, essentially facilitating the transfer of light-generated electrons from the silicon cell to the metallic contact with minimal losses. This results in a higher open-circuit voltage of the solar cells and, consequently, higher cell efficiency.

Operations of TOPCon technology for solar cell

1. Sunlight is incident on the solar cell from the top side (and also from the bottom side in the case of bifacial cells) and gets absorbed in the silicon material.
2. Absorption of sunlight generates electron-hole pairs. The electrons in the valence band absorb the light energy and jump to a higher energy state (the conduction band), in which it can flow freely from atom to atom (not bound to any one atom). Holes are the vacancies left behind in the valence band when the electron jumps to the conduction band. These holes can be considered positive charge carriers (but they move in the valence band in the opposite direction to electrons).
3. At the junction of the P-type and N-type regions, there is an electric field that causes the photo-generated electrons to flow to the N-type region and the corresponding holes to the P-type region. This separates the electron from the hole, which would otherwise recombine to give backlight.
4. These photo-generated electrons that cross the P-N junction region now move to the bottom side of the N-type layer towards the rear contact.
5. Electron-hole pairs are also generated in the bulk (N-type layer). If these holes are present near the rear contacts, then they can cause recombination (as the metal-silicon contact region acts as a powerful recombination centre), leading to the loss of the photo-generated electrons.
6. Here the concept of Tunnel Oxide Passivated Contact (TOPCON) comes into play. The 1-2 nm-thin layer of SiO₂ tunnel oxide acts like a selective gate, allowing only electrons to pass through it to the rear side (and stopping any holes). Further, the n+ polysilicon layer creates an electric field that attracts the electrons and repels the holes. This ensures that a high number of electrons reach the bottom-side silver contacts, where they are collected by the interconnect ribbons and sent to the external load circuit.

Pros of TOPCon Technology

Manufacturing process

It can be manufactured on the same machines as P-type Multi-Busbar modules (like the Mono PERC production lines), which means that the module manufacturers have to bear no additional cost to manufacture TOPCon modules.

Higher efficiency

Compared to P-type Mono PERC cells, TOPCon cells are more efficient at converting solar energy into electricity, increasing both cell and module efficiency. The maximal efficiency of TOPCon cells is 28%, while that of PERC cells is only about 24%.

Lower degradation

In comparison to PERC panels, TOPCon modules exhibit a reduced rate of power degradation both in the first year and throughout the panel’s 30-year operational life.

Lower temperature coefficient

The percentage of power production lost by a solar panel with each degree of temperature increase is known as the temperature coefficient. In hot conditions, it affects the power generation of PV modules.

Since TOPCon cells are less impacted by temperature increases, TOPCon modules’ effectiveness will be higher in hot climates compared to PERC modules.

Bifaciality factor

TOPCon cells have a higher bifaciality factor than PERC modules. It is an important factor as bifacial solar modules are becoming more popular in the market.

Excellent low-light performance

Since TOPCon modules are more efficient in low light, the daytime power generation period is extended, and the annual energy output of the PV system is increased.

Rayzon adopted Topcon technology because it allows for improving the overall performance of the solar panel system, which increases its electricity production by absorbing more photons from the sun’s rays in the highest latitude areas of the earth.

Rayzon Solar is the industry’s future, and we hope this article has given you some useful understanding of Topcon technology. Rayzon Solar is one of the leading manufacturers in the solar sector, adopting cutting-edge TOPCon technology as part of its commitment to sustainability. We urge you to choose solar panels to generate electricity and move from black energy to green energy. Let’s make the future more vibrant and sustainable.