Bifacial solar modules are the industry’s rising stars, promising up to 25% more energy by capturing sunlight from both sides. It’s an elegant concept, but as developers push for higher efficiency and longer lifespans, a hidden weakness is emerging from a place few think to look: the bond between the encapsulant and the transparent backsheet.
Imagine spending millions to develop a high-performance bifacial module, only to see it suffer from premature delamination a few years into its 30-year life. The culprit? A material choice that looked great on day one but couldn’t withstand the relentless assault of ultraviolet (UV) radiation on the module’s rear side.
This isn’t a hypothetical problem. Adhesion—the very glue holding the module’s layers together—can degrade dramatically under real-world conditions. And what’s most alarming is that not all transparent backsheets are created equal.
The Unseen Hero: Adhesion in Bifacial Modules
In any solar module, the layers—glass, encapsulant, solar cells, and backsheet—must remain perfectly bonded for decades. This bond, known as adhesion, is critical. It prevents moisture from creeping in, protects cells from physical stress, and ensures the module remains electrically safe and efficient.
For bifacial modules, the transparent backsheet replaces the traditional opaque one, allowing reflected light to reach the back of the cells. This innovation, however, introduces a new challenge. While a standard backsheet is shielded, a transparent one is constantly exposed to UV radiation. Over time, this exposure can break down the chemical bonds at the surface, weakening its connection to the encapsulant (like EVA or POE).
This gradual degradation is a silent threat that doesn’t show up in initial quality checks. A module can pass every factory test with flying colors, yet harbor a material flaw that will only reveal itself after years in the field.
Putting Materials to the Test: A Comparative Adhesion Study
To understand this risk, we must move beyond datasheet specifications and into the world of applied research. It’s not enough to know how a material performs when new; we need to know how it will behave after being aged by the sun.
At PVTestLab, we conducted a study to compare the adhesion strength of different transparent backsheet materials before and after accelerated UV exposure. We analyzed four distinct types of commercially available transparent backsheets—let’s call them Type A, B, C, and D—each with a different material composition.
Round 1: Adhesion Performance Before UV Exposure
First, we measured the initial peel strength between a standard POE encapsulant and each of the four backsheets. The results, measured in Newtons per centimeter (N/cm), represent the force required to pull the layers apart. A higher number indicates a stronger bond.
All four materials delivered solid initial performance, with Type C showing exceptionally strong adhesion from the start. Based on this data alone, a module developer might conclude that any of these materials are a safe bet. But this is only half the story.
Round 2: The Real Test – Adhesion After UV Exposure
Next, we subjected the same material combinations to an accelerated aging sequence based on the IEC 61215 standard, which simulates the harsh effects of long-term environmental exposure. After this intense UV and damp-heat conditioning, we measured the adhesion strength again.
The results were dramatically different. This is the „aha moment.“ While some materials held up well, others failed spectacularly.
- Type A saw its adhesion drop by nearly 40%, falling to a level that raises concerns about long-term delamination.
- Type B experienced a catastrophic failure, with its adhesion strength plummeting by over 80%. A module built with this backsheet would be at high risk of field failure.
- Type C and D, in contrast, demonstrated remarkable stability. Their adhesion barely changed, proving their material composition is far more resilient to UV degradation.
This is why comprehensive material testing that simulates real-world conditions isn’t just a box to check—it’s fundamental to fulfilling a module’s 30-year performance promise.
What This Means for Your Module Design
The key takeaway is simple but profound: Initial adhesion strength is not a reliable indicator of long-term performance.
For anyone developing, manufacturing, or financing solar projects, this data highlights a critical risk factor. Relying solely on a supplier’s datasheet without conducting independent, post-stress testing is a gamble. The wrong choice of transparent backsheet can turn a high-efficiency module into a long-term liability, leading to underperformance, warranty claims, and significant financial losses.
„In the lab, many materials perform well on paper. But our applied research consistently shows that real-world stressors like UV exposure reveal the true winners and losers. For module developers, testing materials under production conditions isn’t just about quality control—it’s about predicting long-term financial performance.“
– Patrick Thoma, PV Process Specialist at PVTestLab
The path to creating a durable, bankable bifacial module requires validating new solar module concepts with a sharp focus on material resilience. The difference between a successful project and a failed one can come down to the chemical stability of a single, transparent layer.
Frequently Asked Questions (FAQ)
What is delamination and why is it so bad for a solar module?
Delamination is the separation of layers within a solar module. When the backsheet peels away from the encapsulant, it creates a pathway for moisture and oxygen to enter. This can lead to rapid corrosion of the solar cells and internal circuits, causing irreversible power loss and posing serious electrical safety hazards.
Does the type of encapsulant (e.g., EVA vs. POE) affect these results?
Absolutely. While this study used a POE encapsulant, the interaction between the encapsulant and the backsheet is critical. POE is generally known for its lower water vapor transmission rate and resistance to potential-induced degradation (PID), but its adhesion characteristics can differ from EVA. The key is to test the exact combination of materials you plan to use in production.
What does „accelerated UV exposure“ involve?
Accelerated testing uses specialized environmental chambers to simulate decades of outdoor exposure in a matter of weeks or months. For instance, the IEC 61215 standard involves sequences of damp heat (85°C and 85% relative humidity) and UV exposure (irradiance of up to 60 kWh/m²) to stress materials and reveal potential weaknesses that would otherwise take years to appear in the field.
Can other factors besides UV affect backsheet adhesion?
Yes. Extreme temperature cycles (hot days, cold nights), high humidity, and mechanical stress can all contribute to the degradation of the bond between layers. A comprehensive testing protocol should evaluate how materials withstand a combination of these stressors, not just one in isolation.
From Research to Reliability
Choosing the right transparent backsheet is more than a line item on a bill of materials—it’s a long-term investment in your module’s reliability and bankability. As our study shows, the only way to be certain of a material’s performance is to test it under conditions that mirror its life in the field.
By moving beyond datasheets and embracing applied research, you can uncover hidden weaknesses before they become costly field failures. This data-driven approach is the foundation for building next-generation solar modules that not only promise high performance but reliably deliver on that promise for decades to come.
Ready to ensure your material choices are built to last? Explore our approach to solar module prototyping and material validation and see how we help innovators bridge the critical gap between concept and production.