You’ve just pulled a new solar module prototype off the line. It looks perfect—until you catch the light at a certain angle. There it is: a tiny, shimmering bubble trapped near the edge of a solar cell. Is it a harmless cosmetic flaw or a critical defect that could cause the module to fail in the field?
It’s a familiar scenario for countless process engineers and module developers. Lamination voids and air bubbles are among the most common and frustrating defects in solar module manufacturing. They can compromise a module’s long-term performance, durability, and ultimately, its bankability.
The good news is that these defects are not random. They are symptoms of specific issues within the lamination process. By learning to classify them correctly—much like a doctor diagnosing a patient—you can trace them back to their root cause and systematically eliminate them. This guide lays out a framework to do just that, using the industry-standard IEC 61215 criteria as our foundation.
Why Do Bubbles and Voids Form? The Short Answer
At its heart, solar module lamination is about creating a perfectly sealed, weatherproof sandwich. We take a stack of materials—glass, encapsulant (like EVA or POE), solar cells, another layer of encapsulant, and a backsheet—and fuse them together using heat, pressure, and vacuum.
The goal is to remove every trace of air and moisture while melting and curing the encapsulant to form a solid, protective bond. Bubbles and voids are simply pockets of trapped air or gas that failed to escape during this critical PV module lamination process. This failure can almost always be traced back to one of three things: the materials, the pre-processing, or the lamination parameters themselves (temperature, pressure, and vacuum).
Decoding IEC 61215: Your Guide to Lamination Quality
Before we play detective, we need to understand the rules. The International Electrotechnical Commission (IEC) standard 61215 is the „rulebook“ for crystalline silicon module design qualification and type approval. It sets the minimum requirements for quality and tells us which defects are acceptable and which are grounds for failure.
When it comes to lamination voids, IEC 61215 doesn’t just say „no bubbles allowed.“ Instead, it provides a nuanced framework based on three key factors:
-
Location: Where is the void? A bubble floating in the space between cells is far less concerning than one touching a busbar or the edge of the module. Voids in contact with active components can create pathways for moisture ingress, leading to corrosion and delamination over time.
-
Size: How big is it? The standard is clear that some microscopic bubbles may be acceptable. However, research and field data show that voids larger than 1-2 mm, especially those near busbars or cell interconnects, are typically considered critical failures.
-
Quantity and Density: Is it a single, isolated bubble or a cluster? A high density of bubbles, even small ones, indicates a systemic process problem and can significantly reduce the module’s optical performance and long-term stability.
Understanding these criteria is the first step. It helps you move from „there’s a bubble“ to „we have a 3mm void in contact with the busbar, which is a critical failure according to IEC 61215.“
From Symptom to Source: A Root Cause Analysis Framework
With a void properly classified against the IEC criteria, you can begin the root cause analysis. Different types of bubbles point to different process faults, and at PVTestLab, we use the following framework to diagnose the most common issues.
Type 1: Small, Uniformly Distributed Bubbles
- The Symptom: Your module looks like it has a fine „fizz“ of tiny bubbles spread evenly across its surface, often only visible under close inspection.
- The Likely Cause: This is a classic sign of insufficient vacuum. During the initial stages of the lamination cycle, the vacuum pump is responsible for removing all the air from between the layers. If the vacuum level isn’t deep enough or isn’t held for long enough, tiny pockets of residual air get trapped when the encapsulant begins to melt and flow.
- How to Fix It: Review your vacuum pump’s performance, check for leaks in the laminator seals, and consider increasing the duration of the vacuum stage before heat and pressure are applied.
Type 2: Large, Irregular Voids (Often Near Edges or Junction Boxes)
- The Symptom: These are larger, „cloudy“ or amorphous voids that don’t look like simple air bubbles. They are often concentrated near the module’s edges or around the junction box.
- The Likely Cause: This pattern often points to outgassing. As the encapsulant (especially EVA) cures, it produces chemical byproducts. If the temperature ramp-up is too fast or the curing time is too short, these gases don’t have enough time to escape before the encapsulant solidifies, forming large voids. Moisture trapped in the backsheet or other components can also be the culprit.
- How to Fix It: Adjust your temperature profile. Try a slower ramp-up speed or a multi-stage temperature recipe to allow gases to escape. Ensure all materials are stored in a climate-controlled environment to prevent moisture absorption prior to lamination.
Type 3: Bubbles Along Cell Edges or Busbars
- The Symptom: You see distinct bubbles forming a neat line right along the sharp edges of the solar cells or following the path of the interconnect ribbons.
- The Likely Cause: The topography of the module creates tiny „tents“ where air can get trapped. The step-down from the cell surface to the backsheet is a prime location. Flux residues from the soldering process, which can outgas when heated in the laminator, are another common cause.
- How to Fix It: This requires a close look at your materials and layup process. Ensure interconnect ribbons are properly seated and that flux residues are thoroughly cleaned. Sometimes, using a more flexible or higher-flow encapsulant is necessary. This is where comparative material testing services become invaluable, helping you see how different encapsulants behave with your specific cell and ribbon design.
Beyond Diagnosis: The Path to a Perfect Lamination
Identifying the root cause of lamination voids on a live production line can be costly and disruptive. Do you halt production to test a new temperature profile? Do you risk an entire batch of modules on an unverified encapsulant?
This is where an applied research environment becomes essential. At PVTestLab, we provide a full-scale industrial R&D line where developers and manufacturers can troubleshoot these exact issues in a controlled, data-driven setting. Instead of guessing, you can systematically test variables one by one:
- Run back-to-back trials with different vacuum durations.
- Compare three different temperature recipes on the exact same material stack.
- Laminate modules with encapsulants from different suppliers to see which performs best with your design.
Our experienced process engineers help interpret the results, connecting data from the laminator to the final module quality inspection. This approach bridges the gap between theory and real-world production, turning costly guesswork into a clear, actionable optimization plan.
Frequently Asked Questions About Lamination Voids
Can small bubbles get bigger over time?
Yes. Temperature cycling in the field can cause the gas trapped in a bubble to expand and contract, which can stress the surrounding material. Over many years, this can lead to delamination, allowing moisture to penetrate the module.
Are bubbles more common with certain encapsulants like POE vs. EVA?
Not necessarily, but they can be caused by different mechanisms. EVA produces curing byproducts, so outgassing is a primary concern. POE doesn’t have the same curing chemistry, but it can be more sensitive to processing parameters and moisture, leading to voids if not handled correctly.
How do you detect bubbles that aren’t visible to the naked eye?
Electroluminescence (EL) testing is a powerful tool. Voids or delaminated areas can create dark spots or patterns in an EL image, revealing defects that are completely invisible to the eye but can still impact performance.
Is it possible to have a 100% bubble-free lamination?
That’s the goal of every manufacturer. While microscopic imperfections might exist, achieving a visually perfect, void-free lamination that easily passes all IEC 61215 criteria is absolutely achievable with a well-characterized material set and a finely tuned lamination process.
What’s the first step to take if I find bubbles in my production?
Start by documenting and classifying them. Note the size, location, and density. Take high-resolution photos. This data is the first clue in your investigation and is critical for determining whether you have a minor process drift or a critical quality issue.
Understanding these defects is the first step toward creating more reliable and efficient solar modules. The next is optimizing your process to prevent them entirely. For those looking to validate new materials or fine-tune their production recipes, exploring a prototyping and module development environment is a critical step to ensure your innovations are ready for mass production.