Solar panels are constantly evolving and incorporating new technologies to become more efficient at delivering power from the sun.

TOPCon solar panels are taking their place as the dominant solar panels design in the market, taking over from PERC solar cells which were the previous best.

Tunnel oxide passivated contact (TOPCon) solar panels are being advanced for their higher efficiency compared with older PERC solar panels. They are the first n-type solar panels to go into mass production.

Here we will explain what TOPCon technology is and how it is used in solar PV panels

TOPCon solar cell technology is an advancement of the PERC solar cell structure, which was used in the majority of panels until 2024.

They are designed to further reduce surface recombination of cells via the replacement of the back surface field and the addition of an ultra-thin silicon dioxide (SiO2) layer.

This is meant to prevent metal in the connection contacts on the solar panel from coming into contact with the main silicon layer. These contacts are conductive pathways that transfer electricity from the solar cell into the external circuit, where it goes on to power your house.

Below that, the back surface field is replaced with a layer of silicon which has been highly doped with phosphorus. The added passivation from these two features helps to reduce surface recombination.

The layer of SiO2 needs to be thin enough that charge carriers are able to ‘tunnel’ through to the contacts to generate the electric current.

This is important for ensuring that solar panels generate as much electricity as possible, instead of wasting it on electrons that don’t go anywhere. We’ll get into that in more detail below.

TOPCon solar cells were first developed at the Fraunhofer Institute for Solar Energy Systems ISE from 2013 – 2016 as they sought to improve efficiency levels.

However, it was several years after that before solar panels began to be manufactured using the technology.

Solar panels make electricity from light through the photovoltaic effect. The key component, or charge carrier, in this for solar panels is an electron-hole pair.

When light strikes the solar panel, it causes free electrons to become energised and flow along a set path created by the contacts on the panel. This generates an electric current as the electrons flow.

The electron will then eventually return to the panel after passing through the circuit, and recombine with an electron hole, a space that an electron could fill in an atom, and the process repeats.

Surface recombination occurs at the edge of the solar cell and undermines this process. Here, the excited electron fails to generate an electric current because it recombines with an electron hole before leaving the solar cell and entering the circuit.

Recombination losses are a big impediment to improving the efficiency of solar panels, and have been a target of improvements to solar PV technology for years.

TOP Con Solar Modules are typically made of n-type solar cells, where the n-type silicon layer makes up the bulk, and the p-type layer is the emitter at the top of the solar cell.

All solar cells based on silicon have two layers of p-type and n-type. The negatively charged n-type layer has an excess of free electrons to act as charge carriers. The positively charged p-type layer has more electron holes.

Solar panels generate electricity by having free electrons energised and travelling through a circuit created by the front and back contact, creating a current as they do, before combining with an electron hole when they arrive back in the solar cell.

A solar cell is divided between the bulk layer and the emitter layer, with one of each being n-type and the other being p-type. The p-n junction between the two is essential for solar panels to create electricity.

Whether a solar cell is considered an n-type or p-type is determined by which makes up the bulk layer. For a long time, p-type solar panels have dominated the market due to their simpler and cheaper manufacturing. However, n-type panels are taking over due to their superior performance.

In TOPCon solar cells, the lower part of the bulk n-type region is doped with phosphorus to create a back surface field. The tunnel oxide layer is located between that back surface field and the bulk of the n-type layer.

These additions help to significantly reduce recombination in comparison with PERC cell types and improve the efficiency of the solar panels.

There are some potential drawbacks to TOPCon solar panels compared with older tech. However, these were more prominent in the early days of their adoption and have been reduced in the past year or two.

TOPCon solar cells have become the dominant cell type in the market, overtaking PERC in 2024 and projected to achieve over 70% market share in 2026. This trend is expected to continue for the remainder of the decade before they are gradually overtaken by newer technologies.

In that same time period, other technologies such as silicon heterojunction (SHJ) and Back Contact cells are also expected to gain traction in the market. Mass-produced tandem perovskite-silicon cells are also anticipated to enter the market after 2027.

TOPCon solar panels could also become cheaper due to declining quantities of silver used for their contacts over time. Market predictions currently expect the amount of silver used in a TOPCon solar cell to fall from 120mg per cell in 2023 to under 80mg by 2034.

However, as solar panels consume ever greater quantities of the world’s silver supplies, this might also lead to price increases for the material, which would hopefully be offset by other improvements in the manufacturing process.