The solar industry is buzzing with the promise of n-type TOPCon (Tunnel Oxide Passivated Contact) cells, and for good reason. Their potential for higher efficiency is pushing photovoltaic performance to new heights. But as with any major technological leap, this new frontier comes with its own challenges—one of which can silently sabotage a module’s performance over its lifetime.
We’re talking about Potential-Induced Degradation, or PID. While PID isn’t a new problem, TOPCon technology introduces a new, more aggressive variant: PID-p, where the ‚p‘ stands for polarization. For module manufacturers navigating this transition, understanding and mitigating this risk isn’t just a quality check; it’s fundamental to ensuring the long-term bankability of their products.
The key to winning this battle lies in a component that is often overlooked: the encapsulant. This isn’t just the „glue“ holding the module together; it’s the first line of defense against electrical and environmental stress. Today, we’re exploring how two advanced encapsulants, POE and EPE, stack up in a head-to-head test against PID-p.
The New PID on the Block: Why TOPCon Changes the Game
For years, the industry has focused on PID in traditional p-type PERC cells. This typically occurs when a negative voltage potential relative to the grounded module frame causes sodium ions to migrate into the cell, leading to shunting and a gradual loss of power.
However, n-type TOPCon cells flip the script.
Due to their different doping structure, they are susceptible to a polarization effect (PID-p) under a positive voltage potential. This effect can cause a much more rapid and severe power loss than traditional PID if not properly managed. The TCO (Transparent Conductive Oxide) layers, critical to TOPCon’s high efficiency, are particularly vulnerable to this degradation mechanism.
This fundamental shift means that materials and processes proven for PERC modules may not be sufficient for TOPCon. The entire Bill of Materials (BOM), especially the encapsulant, must be re-evaluated to guarantee 25+ years of reliable field performance.
The Encapsulant’s Role: More Than Just a Laminate
The encapsulant’s primary job is to provide electrical insulation between the solar cells and the rest of the module package. Its electrical resistivity is what prevents the leakage currents that can trigger PID.
Here’s where the material science comes in:
- Standard EVA (Ethylene Vinyl Acetate): The long-time industry workhorse, EVA is known for its excellent adhesion and processability. However, it can produce acetic acid as a byproduct, which lowers its volume resistivity and makes it more susceptible to moisture ingress—two factors that accelerate PID.
- POE (Polyolefin Elastomer): POE is inherently resistant to PID due to its non-polar nature and high electrical resistivity. It also boasts an extremely low water vapor transmission rate (WVTR), preventing moisture from compromising the module’s internal components. The trade-off? POE can be more challenging to process, often requiring longer lamination cycles.
- EPE (Extruded Polyolefin Elastomer): EPE is a hybrid, multi-layer encapsulant that aims to deliver the best of both worlds. It typically features a core layer of EVA for strong adhesion, sandwiched between two outer layers of POE. This design provides the PID resistance of POE with processing ease closer to that of traditional EVA.
For a TOPCon manufacturer, the choice between POE and EPE is a critical decision that balances long-term reliability with production efficiency. But how do they perform under real-world stress?
Putting Theory to the Test: A Real-World PID-p Showdown
To get a clear, data-driven answer, we designed a comparative test at PVTestLab. The goal was to simulate decades of harsh field conditions to see how POE and EPE encapsulants protect n-type TOPCon modules from PID-p. We built two sets of glass-glass modules on our industrial-grade R&D line, with the only variable being the encapsulant material. Isolating a single variable like this is central to effective solar module prototyping and key to delivering clean, actionable data.
The Test Setup
The modules were subjected to high-voltage stress in a climate chamber, following the industry benchmark IEC TS 62804-1-1 standard.
The conditions were designed to be aggressive:
- Voltage: -1500 V applied to the module surface, creating a high positive voltage potential from the cells to the grounded frame
- Temperature: 85°C
- Relative Humidity: 85%
- Duration: 192 hours (two full 96-hour cycles)
Before and after the stress test, each module underwent a full characterization, including I-V flash testing to measure power output and electroluminescence (EL) imaging to visually inspect for cell damage.
The Verdict: How Did POE and EPE Perform?
The results were definitive and encouraging. Both the POE and EPE encapsulants demonstrated outstanding resistance to PID-p.
Power Degradation: After 192 hours under intense heat, humidity, and voltage stress, the power degradation for modules using both types of encapsulants was less than 1%. This is well below the typical 5% failure threshold, proving their effectiveness in protecting the TOPCon cells.
Visual Inspection: The EL images supported the power measurements. Post-test images showed no signs of newly formed dark areas or shunting, which would typically indicate PID-related cell damage. The cells were as healthy as they were before the test began.
Image: Electroluminescence (EL) images comparing a module before and after PID testing, showing minimal degradation.
So, if both materials passed with flying colors, how does a manufacturer choose? This is where process expertise becomes critical.
As Patrick Thoma, a PV Process Specialist at PVTestLab, explains, „While both materials performed exceptionally well against PID-p, the processability during lamination is where the decision-making gets nuanced. EPE’s compatibility with existing EVA lamination cycles can offer a significant advantage in production efficiency. However, for applications demanding the absolute lowest water vapor transmission rate, pure POE remains the gold standard. The right choice often comes down to balancing these factors, which is why conducting targeted lamination process trials is so important.“
Beyond PID: What This Means for Your Production Line
This test confirms that high-quality POE and EPE encapsulants are non-negotiable for producing reliable, long-lasting n-type TOPCon modules. The choice between them isn’t about good vs. bad, but about finding the right fit for your specific production line and product goals.
Factors to consider include:
- Process Integration: Can your existing laminators handle the cycle times and temperatures required for pure POE, or would an EPE encapsulant allow for a smoother, faster integration?
- Bill of Materials (BOM) Compatibility: How does the encapsulant interact with your chosen backsheet, glass, and other components?
- Supply Chain & Cost: Are both materials readily available from your trusted suppliers, and how do they impact the final module cost?
Answering these questions requires moving beyond datasheets and into the realm of applied research. By evaluating new solar module materials under real industrial conditions, you can de-risk the transition to TOPCon and ensure your final product delivers on its promise of higher efficiency and long-term reliability.
Frequently Asked Questions (FAQ)
What is PID in simple terms?
Potential-Induced Degradation (PID) is a slow power loss in solar panels caused by leakage currents. It occurs when there’s a large voltage difference between the solar cells and the module frame, especially in hot and humid conditions, causing ions to migrate in ways that degrade the cell’s performance.
Why is PID-p a specific concern for TOPCon modules?
TOPCon modules use n-type solar cells, which have a different electrical structure than traditional p-type cells. This makes them vulnerable to a „polarization“ effect (PID-p) when the cells have a positive voltage relative to the frame. This type of degradation can be faster and more severe than the PID seen in older p-type modules.
What’s the main difference between POE and EPE encapsulants?
POE is a single material (Polyolefin Elastomer) known for its excellent electrical insulation and moisture resistance. EPE is a multi-layer composite, typically with a core of adhesive-rich EVA and outer layers of protective POE. EPE is designed to combine the PID resistance of POE with the easier processing of EVA.
Is EVA obsolete for TOPCon modules?
While some PID-resistant EVA formulations exist, standard EVA is generally not recommended for n-type TOPCon modules due to its lower electrical resistivity and potential to generate acetic acid, which can accelerate degradation mechanisms. Advanced encapsulants like POE or EPE are considered the safer, more reliable choice.
How long does a typical PID test take?
A standard PID test, as defined by IEC standards, typically runs for 96 hours. In our comparative test, we ran two full cycles for a total of 192 hours to subject the modules to an even higher level of stress and gain deeper confidence in the materials‘ long-term stability.
The Path to Reliable Innovation
The transition to n-type TOPCon technology is an exciting step forward for the solar industry. However, harnessing its full potential requires a rigorous approach to material selection and process validation. As our test shows, advanced encapsulants like POE and EPE are essential tools for mitigating the inherent risk of PID-p and ensuring modules perform reliably for decades.
Understanding how these materials behave on your specific production line is the critical next step. A controlled testing environment allows you to validate performance, optimize your manufacturing process, and move from concept to mass production with confidence. To see how this is done, explore the capabilities of PVTestLab’s R&D production line, where research meets real production.