Like HJT and IBC cells, TOPCon technology (Tunnel Oxide Passivated Contact) belongs to the category of so-called type-N cells, which use phosphorus-doped silicon wafers, unlike type-P cells, which are still dominant in the market in 2023 and are gallium-doped.
This difference in the manufacturing process provides a clear advantage to type-N cells in terms of potential efficiency, as shown in the graph below.
During the conversion of cells into modules, an inevitable drop in efficiency is primarily due to the absorption and reflection of light by the upper layers (glass and encapsulation) and the presence of inactive surfaces between the cells and at the module's edges. However, the efficiency of TOPCon modules remains higher than that of PERC modules.
This superior efficiency, combined with the properties described in the table below, makes TOPCon photovoltaic panels a particularly compelling solution compared to PERC technology, which belongs to the P-type category and was the most widespread between 2018 and 2023.
Comparison of PERC and TOPCon technology
|Minimum guaranteed efficiency||Between 20.5% and 21%||Between 21.5% and 22%||A higher efficiency enables the installation of a greater power output for the same panel surface area, which is a crucial factor for residential applications. This translates to an approximate gain of 15 to 20 watts peak (Wp) per residential panel.|
|Initial loss due to light exposition (LID)||Between 0.5% and 1%||0%||"Several days after installation, a power loss attributed to Light-Induced Degradation (LID) is observable on Type P modules, but not on Type N modules."|
|Percentage of initial power after 30 years||85%||87.4%||"TOPCon modules exhibit better durability and demonstrate lower power degradation throughout their 30-year lifespan in solar panels."|
|Power temperature coefficient||-0.33||-0.31||The temperature coefficient allows us to assess the power loss of a solar panel for every additional degree. This coefficient is lower in the case of TOPCon cells, which means that these panels will have better performance than PERC panels as the temperature rises.|
|A bifacial module generates electricity on both of its sides. A higher bifaciality rate results in increased electricity production on the rear side of the cells.|
The values above are provided for reference and may vary from one model to another.
The combined effect of these TOPCon advantages results in an energy production gain ranging from 1.5% to 5% compared to a PERC module with the same nominal power, depending on local climatic conditions, module specifications, and the installation system.
The manufacturing of TOPCon modules differs from PERC in terms of ingot and cell production. There are opportunities to convert PERC production lines to TOPCon with a reasonable capital expenditure (CapEx). The module assembly line, on the other hand, is nearly identical for both PERC and TOPCon.
However, it is important to note that due to the increased sensitivity of TOPCon cells to moisture, most modules built with this technology have a hermetic glass-glass structure. Nevertheless, it is possible to manufacture TOPCon modules with a glass-polymer film structure by ensuring the selection of an encapsulation material with adequate moisture resistance properties.
A TOPCon module is significantly more expensive per peak watt than PERC (+5% to 10% as of September 2023) for two main reasons:
- The cost of Type N wafers is higher than Type P wafers. This is partly due to a less uniform dopant distribution in Type N ingots compared to Type P, resulting in a non-negligible proportion of Type N ingots that cannot be converted into wafers and must be discarded.
- The amount of silver, a highly costly material, used in TOPCon cells on both the front and rear sides is greater than in PERC cells, which only contain silver on the front side.
This price difference has already been significantly reduced since 2022 and is likely to continue to decrease. TOPCon is projected by most analysts to become the dominant photovoltaic module technology in 2024, likely accounting for over 50% of modules produced that year.
To go further :
One can consider TOPCon solar cells as an advanced version of traditional solar cells (PERC). The hallmark of this technology is its significant reduction of energy losses that typically occur at the metal contacts and silicon surface in conventional solar cells. This is made possible through a thin tunnel oxide layer covering the entire surface of the solar cell, in addition to a highly 'doped' polycrystalline silicon layer with phosphorus atoms placed between the metal contacts and the silicon wafer.
This doping process adds extra electrons to the material, creating a region with an excess of electrons. When sunlight hits this doped region, the absorbed photons release free electrons that can then move to generate an electric current. These elements contribute to a more efficient conversion of solar energy into electricity, making solar energy more competitive and sustainable
The front-side metallization of TOPCon cells is composed of a silver-aluminum alloy. Some studies have pointed out the alloy's higher sensitivity to humidity compared to PERC cells, which necessitates measures to ensure a hermetic encapsulation of the cells. One of the solutions chosen is to use a glass-glass structure, often paired with a specific encapsulant like POE (polyolefin elastomer), to provide better resistance to moisture penetration than in the case of a traditional glass-EVA-polymer film backsheet structure.
What is TOPCon technology?
TOPCon solar cells can be considered an evolved version of traditional solar cells (PERC).
The characteristic of this technology is that it considerably reduces the energy losses which generally occur at the metal contacts and at the surface of the silicon in the traditional solar cells.
This is possible thanks to a thin tunnel oxide layer that covers the entire surface of the solar cell, in addition to a layer of highly "doped" polycrystalline silicon with phosphorus atoms between the metal contacts and the silicon wafer.
TOPCon technology belongs to the category of n-type cells, which uses silicon wafers doped with phosphorus: this doping makes it possible to add additional electrons to the material, thus creating a region with an excess of electrons. When sunlight strikes this doped region, the absorbed photons release free electrons which can then move to create an electric current.
These elements thus contribute to a better conversion of solar energy into electricity, for a more competitive and sustainable solar energy.
> To go further : What are the advantages of DualSun SPRING and FLASH shingle panels ?