A new type of degredation found in TOPCon : should you be worried ?

A new type of degredation found in TOPCon : should you be worried ?

​TOPCon Technology (Tunnel Oxide Passivated Contact) has gradually established itself as the dominant technology in the photovoltaic market, driven by significant advancements in conversion efficiency and economic competitiveness. However, this rise in popularity is accompanied by growing concerns regarding the long-term reliability of TOPCon modules, particularly in hot and humid environments.
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Recent studies highlight the increased sensitivity of the front side of TOPCon cells to corrosion, exacerbated by exposure to contaminants from the glass, such as NaCl or NaHCO₃. These contaminants can be present from the manufacture of the glass (AR layers / soda-lime glasses) or penetrate on site (via dust / pollutants / sea air). Accelerated aging tests (such as "Damp Heat") reveal a significant increase in series resistance, resulting in substantial power losses and compromising the durability of the modules. Several approaches, including laser-assisted metallization or the use of new low-aluminum screen-printing pastes, are being explored to enhance the resilience of cells against external aggressions.

Simultaneously, the choice of encapsulation materials and module structure (glass/backsheet vs. bifacial glass) plays a key role in preserving the performance of TOPCon modules. While traditional polymer backsheets (PET, polyolefin) offer appreciable lightness and flexibility, they expose cells to increased risks of degradation due to humidity and corrosive by-products like acetic acid, resulting from EVA degradation. Conversely, bifacial glass modules, although heavier, demonstrate better resistance to moisture infiltration and chemical aggressions, thereby extending the lifespan of photovoltaic systems.

In this context, the question of optimizing TOPCon module design remains open: how can we balance performance, cost, and reliability to ensure a sustainable technological transition? This challenge requires a thorough analysis of the interactions between metallization, encapsulation, and operating environment to guide the development of robust and durable solutions for the next generation of photovoltaic modules.
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To better understand the degradation mechanisms involved, a diagram detailing the root causes, the sequence of chemical and physical reactions, and their final consequences
 on the performance of photovoltaic panels is presented below:



The choice of encapsulant plays a determining role in the degradation process. Here is a quick comparison of its effects on degradation and the impact on energy production:



The choice of backsheet type (or its absence in favor of a dual-glass module) strongly influences the degradation process. Here is a quick comparison of the different options, highlighting their consequences on degradation and the impact on energy production:



The photovoltaic industry is actively investigating this new type of degradation, which initially raised concerns among professionals regarding the long-term viability of this technology. Several levers can be used to mitigate these issues, including the following:
  1. Opting for bifacial glass modules or selecting a well-matched encapsulant/backsheet
     combination. You can consult our knowledge base, where we already have an in-depth article discussing the advantages and disadvantages of bifacial glass compared to glass/backsheet modules.
  2. The TPO-CPO combination
     appears to minimize long-term degradation while maintaining strong energy production.
  3. A recent innovation, LECO (Laser-Enhanced Contact Optimization), enables lower-temperature metallization, reducing or even eliminating the need for aluminum, thereby limiting corrosion effects. Jinko
     has already implemented "Laser-assisted fire processing" during metallization, allowing them to reduce aluminum content by 90%.
  4. Another approach suggests placing an ultra-thin copper layer
     (~1 μm) over the Ag/Al contacts to create a better interface and prevent corrosion/delamination. In Damp Heat tests with added NaCl, coated cells lost about 11.5% efficiency compared to around 80% for uncoated cells.
  5. Back-Contact (xBC) modules offer another alternative, as their specific design consolidates all metal contacts at the rear, fully encapsulated, significantly reducing corrosion risks. 
Despite the challenges associated with TOPCon degradation, this technology remains undeniably promising for the future of solar energy. The photovoltaic industry is implementing technical solutions to overcome these limitations, much like the progress made with PERC technology, which successfully addressed issues related to BO-LID (Boron-Oxygen Light-Induced Degradation) and LeTID. These innovations will further enhance the long-term reliability and efficiency of TOPCon. However, due to the identified risks of corrosion and moisture degradation, many manufacturers have moved away from glass/backsheet modules, which, although lightweight, offer less protection. This is why we have chosen to only offer dual-glass modules, ensuring better durability and reliability. To explore our TOPCon offerings, we invite you to visit our PV module catalog. on the Synapsun portal.

References: 
  1. Wiley Online Library (11/2024), Reliability of Commercial TOPCon PV Modules—An Extensive Comparative Study, available on: https://onlinelibrary.wiley.com/doi/full/10.1002/pip.3868
  2. ScienceDirect (08/2024), Buyer aware: Three new failure modes in TOPCon modules absent from PERC technology, available on: https://www.sciencedirect.com/science/article/pii/S0927024824001892
  3. PV Magazine (12/2024), Fraunhofer ISE warns of risk from higher than expected UV-induced degradation in TOPCon, PERC, HJT cells, available on: https://www.pv-magazine.com/2024/12/02/fraunhofer-ise-researchers-warn-of-risk-from-higher-than-expected-uv-induced-degradation-in-topcon-perc-hjt-solar-cells/
  4. Wiley Online Library (02/2023), Quantifying the influence of encapsulant and backsheet composition on PV-power and electrical degradation, available on: https://onlinelibrary.wiley.com/doi/full/10.1002/pip.3679
  5. ScienceDirect (12/2024), Unveiling the origin of metal contact failures in TOPCon solar cells through accelerated damp-heat testing, available on: https://www.sciencedirect.com/science/article/pii/S0927024824005002
  6. ScienceDirect (07/2023), Corrosion effects in bifacial crystalline silicon PV modules; interactions between metallization and encapsulation, available on: https://www.sciencedirect.com/science/article/abs/pii/S0927024823001423?via%3Dihub
  7. ScienceDirect (01/2023), Impact of acetic acid exposure on metal contact degradation of different crystalline silicon solar cell technologies, available on: https://www.sciencedirect.com/science/article/abs/pii/S0927024822005062?via%3Dihub
  8. ScienceDirect (07/2024), Enhancing the reliability of TOPCon technology by laser-enhanced contact firing, available on: https://www.sciencedirect.com/science/article/pii/S0927024824001582#bib21
  9. ScienceDirect (01/2025), Alleviating contaminant-induced degradation of TOPCon solar cells with copper plating, available on: https://www.sciencedirect.com/science/article/pii/S0927024825000455
  10. ScienceDirect (07/2023) Corrosion effects in bifacial crystalline silicon PV modules; interactions between metallization and encapsulation, available on: https://www.sciencedirect.com/science/article/abs/pii/S0927024823001423