Imagine launching a new line of high-efficiency N-Type TOPCon solar modules. They boast incredible performance on day one, but a few years into their 25-year lifespan, reports of unexpected power loss start trickling in. The culprit? A silent, invisible saboteur known as Potential Induced Degradation, or PID.
For developers and manufacturers pioneering advanced cell technologies, this isn’t a distant threat—it’s a critical engineering challenge. Especially with the move to 1500V systems, the materials you choose to protect your cells matter more than ever. The encapsulant, often viewed as a simple adhesive layer, is actually your primary defense against catastrophic field failures. But not all encapsulants are created equal.
What is Potential Induced Degradation (PID)? A Quick Refresher
Think of PID as a slow electrical corrosion. In large-scale solar arrays, a high voltage potential can build up between the solar cells and the module’s grounded frame. Over time, this voltage stress can cause ions—particularly pesky sodium ions from the glass—to migrate where they don’t belong.
This migration creates leakage paths across the cell, effectively short-circuiting a portion of its power-generating capacity. The process is dramatically accelerated by three key factors present in almost every solar installation:
- High System Voltages (up to 1500V)
- High Temperatures
- High Humidity
The result is a steady, and sometimes rapid, decline in the module’s power output that jeopardizes a project’s financial returns and the manufacturer’s reputation.
The N-Type TOPCon Challenge: A Higher Sensitivity to Shunting
While PID affects most solar cell types, N-Type TOPCon cells have a specific vulnerability: they are highly sensitive to a failure mode called PID-s (shunting). This is where migrating sodium ions move directly through the encapsulant and create tiny electrical shunts across the cell’s delicate structure.
This isn’t just a minor dip in efficiency; it can lead to devastating power loss. The industry’s primary defense against this threat is an encapsulant that acts as a fortress, blocking ion migration. The strength of this fortress is defined by a key property: volume resistivity. An encapsulant with high volume resistivity is like a dam holding back ions, while one with low resistivity is more like a leaky sieve.
The First Line of Defense: Putting Encapsulants to the Test
To ensure long-term reliability, manufacturers need data, not just datasheets. That’s why a direct, head-to-head comparison under harsh, accelerated conditions is so crucial. At PVTestLab, we designed a benchmark test to reveal the true performance difference between a standard Polyolefin Elastomer (POE) encapsulant and a high-resistivity POE designed specifically for PID protection.
Our team specializes in Material Testing & Lamination Trials, where we validate these critical properties under real manufacturing conditions—providing the certainty needed before committing to a full production run.
We started by building two identical glass-glass N-Type TOPCon modules. The only difference was the encapsulant:
- Module A: Laminated with a standard-grade POE.
- Module B: Laminated with a high-resistivity POE.
Both modules were then subjected to PVTestLab’s accelerated PID test protocol in a climate chamber set to 85°C, 85% relative humidity, and a negative voltage of -1500V. Performance was measured at 96 hours and 192 hours using two key diagnostic tools:
- Electroluminescence (EL) Imaging: This acts like an X-ray for solar modules, revealing inactive or damaged areas as dark spots.
- I-V Curve Tracing (Flash Tests): This measures the module’s actual power output under standard test conditions.
The Results: A Tale of Two Modules
The outcome was a stark, unambiguous demonstration of why encapsulant choice is mission-critical.
Standard POE: A Rapid Decline
The module with standard POE began showing signs of trouble after just 96 hours. EL imaging revealed the clear formation of shunts, and the module had already lost over 5% of its initial power. After 192 hours, the degradation was catastrophic, with widespread shunting rendering large sections of the cells useless.
![Electroluminescence image of a TOPCon solar module with standard POE after a 192-hour PID test, showing significant dark areas indicating severe shunting and power loss.]
This is the kind of failure that can silently erode the performance of an entire solar farm.
High-Resistivity POE: A Story of Stability
In stark contrast, the module built with high-resistivity POE remained virtually unharmed. After the full 192-hour test under the exact same brutal conditions, it exhibited less than 1% power loss. The EL image remained clean and uniform, showing that the encapsulant had successfully blocked ion migration and protected the cells.
![Electroluminescence image of a TOPCon solar module with high-resistivity POE after a 192-hour PID test, showing a clean, uniform appearance with no signs of shunting or degradation.]
The visual and electrical data tell a clear story: the high-resistivity POE provided superior ion-blocking capability, preserving the module’s performance and long-term reliability.
![A comparative line graph showing power degradation over time for two TOPCon modules. The blue line (Standard POE) shows a sharp decline, while the green line (High-Resistivity POE) remains stable.]
The Verdict: High-Resistivity POE is Non-Negotiable for TOPCon
This benchmark confirms that for N-Type TOPCon modules in 1500V systems, selecting a high-resistivity POE is essential for long-term reliability and bankability. The difference in performance is not incremental; it’s the difference between a durable, high-value asset and a potential liability.
As our PV Process Specialist, Patrick Thoma, often states:
„For TOPCon, it’s not just about choosing POE; it’s about choosing the right POE. Our tests provide the data-backed confidence that manufacturers need to prevent catastrophic field failures. High volume resistivity isn’t a feature—it’s a requirement.“
Validating these designs early through Prototyping & Module Development is a critical step that can save millions in warranty claims and protect your reputation for quality.
Frequently Asked Questions (FAQ)
What exactly is „volume resistivity“ in an encapsulant?
Think of it as electrical insulation. It’s a material’s inherent ability to resist the flow of electrical current (or in this case, ions). A higher value means better insulation and a stronger barrier against ion migration.
Does this PID issue affect other cell types like PERC?
Yes, PID can affect PERC and other cell types, but the specific PID-s (shunting) mechanism is a particularly acute problem for N-Type TOPCon cells due to their surface structure, which makes them more sensitive.
Is POE always better than EVA for PID resistance?
Generally, POE has a natural advantage over Ethylene Vinyl Acetate (EVA) because its chemical structure is non-polar, making it more resistant to moisture and ion movement. However, as our test shows, the critical factor is the grade of the material. A high-resistivity POE is vastly superior to a standard one for protecting sensitive cells like TOPCon.
Can’t you just use anti-PID glass or frames to solve the problem?
While components like sodium-free glass can help, they don’t eliminate the source of ions entirely. The encapsulant remains the most critical barrier protecting the cell itself. A multi-faceted approach is best, but a high-resistivity encapsulant is the cornerstone of PID prevention for TOPCon.
Your Path to PID-Resistant Module Design
The leap to next-generation cell technologies like TOPCon brings immense opportunities for higher efficiency and performance. However, it also introduces new challenges that demand a deeper understanding of material science and their interactions.
This benchmark underscores a crucial takeaway: your choice of encapsulant is a fundamental design decision, not a simple procurement item. Understanding how your specific bill of materials performs under the stress of high voltage, heat, and humidity is the first step toward building truly reliable modules that will perform for decades.