TOPCon Photovoltaics: Technology, Market Share, Advantages, and Challenges
TOPCon (Tunnel Oxide Passivated Contact) photovoltaic modules are poised to become the dominant technology in the solar sector, marking the end of PERC’s long-standing supremacy. According to a recent report, this segment has seen rapid market share growth, rising from 10% in 2022 to approximately 30% in 2023. Despite PERC still holding the majority (64%) in 2023, the tides are expected to turn in 2024, with TOPCon predicted to capture 50% of the market.
Alongside contributions from SHJ (Silicon Heterojunction) and IBC (Interdigitated Back Contact) technologies—projected to secure a combined 19%—this shift would reduce PERC’s share to just 21% of the global photovoltaic market.
Amid this rapid growth, a key question arises: how reliable are TOPCon solar panels? A new German study from the Fraunhofer Institute for Solar Energy Systems (ISE) sheds light on the matter, examining 20 Tunnel Oxide Passivated Contact modules produced by various manufacturers. The findings? Certain degradation issues still need to be addressed.
Let’s take a closer look.
What Is TOPCon Technology?
TOPCon (Tunnel Oxide Passivated Contact) is a photovoltaic technology developed by the Fraunhofer ISE in 2013. The acronym refers to a structural solution designed to reduce charge carrier recombination while improving charge transport efficiency.
At its core, the technology introduces two key elements to the conventional solar cell architecture:
- A tunnel oxide layer: an ultra-thin (1–2 nanometers) silicon oxide (SiO₂) layer placed between the metal contacts and the silicon wafer. This layer passivates the wafer’s surface, minimizing surface recombination of charge carriers, while its thinness allows electrons to pass through via a tunneling effect.
- A highly doped polycrystalline silicon layer: deposited on top of the tunnel oxide, this layer enhances electrical conductivity and reduces transmission losses.
N-Type TOPCon Photovoltaics
Like all solar cells, TOPCon cells can be classified as P-type or N-type, depending on whether they are doped with atoms that have fewer electrons (P-type) or extra electrons (N-type) compared to silicon. Historically, P-type cells dominated the market due to easier manufacturing processes. However, many manufacturers are now shifting to N-type cells due to their superior efficiency and reliability.
N-type TOPCon technology offers:
- Reduced power degradation: N-type cells are less prone to power-induced degradation (PID).
- Enhanced temperature resistance: These cells maintain performance under higher temperatures.
- Lower sensitivity to metallic impurities: N-type silicon is more resilient against contamination compared to P-type.
Advantages of N-Type TOPCon Photovoltaics
The rapid growth of N-Type TOPCon technology stems from several key benefits:
- Lower recombination losses: The tunnel oxide layer significantly reduces electron-hole recombination.
- Improved charge collection: The polycrystalline silicon layer provides a low-resistance pathway for electrons.
- Higher voltage: Reduced recombination translates to higher open-circuit voltage (Voc).
- Superior conversion efficiency: TOPCon solar cells have achieved a record efficiency of 26.1%, compared to 23.2% for traditional PERC cells.
- Lower degradation rates: Using phosphorus-doped silicon instead of boron eliminates degradation caused by boron-oxygen complexes.
How Does TOPCon Differ from PERC?
Compared to PERC (Passivated Emitter and Rear Cell) technology, TOPCon involves two to three additional manufacturing steps:
- Deposition of the ultra-thin tunnel oxide layer.
- Deposition of an intrinsic passivation layer of polycrystalline silicon.
- Phosphorus doping.
These extra steps contribute to TOPCon’s enhanced performance but also slightly higher production costs.
Degradation Issues
A recent German study by the Fraunhofer Institute for Solar Energy Systems (ISE) provided a detailed evaluation of TOPCon module performance, uncovering critical degradation challenges during accelerated aging tests.
- UV-related degradation: Tests showed significant performance losses of up to 12% after 120 kWh/m² UV exposure. Interestingly, this was followed by partial recovery during moisture-freeze testing, suggesting complex interactions affecting outdoor performance and certification outcomes.
- Moisture-related degradation: These issues appear linked to metallization paste sensitivity, which may be addressed in future TOPCon module designs.
This research highlights the need for targeted testing and technological refinements to ensure TOPCon’s long-term reliability.
For further details, the study is available in Progress in Photovoltaics.
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