You’ve done everything right. You’ve selected high-efficiency cells, sourced a cutting-edge fast-curing POE encapsulant, and designed a state-of-the-art large-format solar module. On paper, it’s a masterpiece of performance and durability.
But what if a single, overlooked detail in your manufacturing process could undermine it all, creating hidden defects that silently degrade power output over the module’s lifetime?
For many manufacturers, that silent killer is the vacuum draw-down rate during lamination. The push for faster cycle times often leads to aggressive vacuum profiles that, while speeding up production, can trap microscopic bubbles in the module stack. These bubbles might be invisible to the naked eye, but they are ticking time bombs for long-term reliability.
It turns out the journey to vacuum—not just the destination—is what can make or break your module’s performance.
Outgassing: The Invisible Challenge in Module Lamination
Every solar module is a sandwich of different materials: glass, encapsulant, solar cells, and a backsheet. The solar module lamination process uses heat and pressure to bond these layers into a single, durable unit that can withstand decades in the field.
A critical step in this process is pulling a vacuum to remove all air and volatile organic compounds (VOCs) from the module stack. This step, known as outgassing, is essential for a perfect, void-free lamination.
However, modern module designs introduce new challenges:
- Large-Format Modules: The bigger the module, the longer the path gases must travel to escape from the center.
- Fast-Curing Encapsulants (POE): These materials cure quickly under heat, meaning the window to remove trapped gases is much shorter. If the encapsulant starts to cross-link before all gases have escaped, they become permanently trapped.
When you combine large formats with fast-curing materials, a standard, single-step vacuum profile can become a recipe for disaster. It pulls a vacuum so quickly that the encapsulant on the edges may begin to cure and seal the escape routes before the gases in the middle have had a chance to evacuate. The result? Micro-bubbles.
A Tale of Two Modules: A Side-by-Side Comparison
To measure the real-world impact of the vacuum profile, we conducted a direct comparison. We built two identical M10, 108-cell modules using the same Bill of Materials (BOM), including a popular fast-cure POE encapsulant. The only variable was the lamination vacuum profile.
- Module A was laminated using a standard, aggressive single-step vacuum profile.
- Module B followed an optimized, multi-step vacuum profile designed to allow more time for outgassing.
Both modules were then subjected to Electroluminescence (EL) testing and flash testing to measure their initial power output (Pmax). Afterward, they underwent a 2,000-hour Damp Heat (DH) test—an accelerated aging process that simulates decades of harsh environmental exposure.
The Results of the Standard Vacuum Profile (Module A)
Immediately after lamination, the EL imaging for Module A revealed a troubling pattern. The module was riddled with micro-bubbles, particularly visible around the cells and interconnecting ribbons.
While these bubbles might seem minor, their impact became clear after the DH2000 test.
- Pmax Degradation: 5.3%
- Post-DH EL Image: The bubbles became more pronounced, indicating that moisture and heat had exacerbated the initial defects.
A power loss of over 5% from a correctable process error is a significant blow to a module’s bankability and long-term energy yield. This aggressive vacuum profile had created permanent, performance-degrading flaws from day one.
The Results of the Optimized Vacuum Profile (Module B)
Module B, which used a gentler, multi-step vacuum draw-down, told a completely different story. The initial EL image was pristine—no signs of micro-bubbles or trapped gases.
The performance after the grueling DH2000 test confirmed the quality of the lamination.
- Pmax Degradation: 2.1%
- Post-DH EL Image: The module remained free of bubble-related defects.
By simply changing the way the vacuum was applied, we cut the power degradation by more than half, preserving the module’s performance and ensuring its long-term reliability.
„This experiment is a perfect illustration of a core principle we see daily at PVTestLab,“ notes Patrick Thoma, a PV Process Specialist. „The best materials in the world can’t compensate for a suboptimal process. The lamination recipe is just as critical as the Bill of Materials for producing a module that will perform reliably for 25+ years.“
From Insight to Action: What This Means for Your Production
The evidence is clear: the vacuum profile isn’t just a setting to be optimized for speed. It’s a critical process parameter that directly influences module quality and longevity.
- Re-evaluate Your Vacuum Profiles: If you are using large-format modules or fast-curing encapsulants, a single-step vacuum is a high-risk approach. Implementing a multi-step profile, with pauses at intermediate vacuum levels, gives gases the time they need to escape properly.
- Validate, Don’t Assume: Whenever you introduce a new material or module design, your existing process parameters must be re-validated. Comprehensive material testing for PV modules should always include process validation to ensure compatibility and prevent issues like outgassing.
- Invest in Prototyping: The cost of discovering a fundamental process flaw after ramping up production is enormous. Investing time in prototyping new solar module designs in a controlled environment allows you to de-risk your process, perfect your lamination recipe, and ensure your final product meets its performance targets.
Frequently Asked Questions (FAQ)
What exactly is „outgassing“ in a solar module?
Outgassing is the release of trapped gases from the materials within the solar module stack during the heated lamination cycle. These gases can come from solvents in the encapsulant, residue from cell manufacturing (like flux), or moisture trapped between layers. The vacuum pump is supposed to remove them, but if the process is too fast, they get stuck.
Why are micro-bubbles such a serious problem?
Micro-bubbles are more than just cosmetic blemishes. They can:
- Compromise Electrical Insulation: A bubble can create a pathway for electrical current to arc between the cell and the frame, leading to potential-induced degradation (PID) or safety issues.
- Create Points for Delamination: Bubbles act as stress concentrators. Over time, thermal cycling in the field can cause the layers to separate (delaminate) around the bubble, allowing moisture to penetrate and corrode the cells.
- Reduce Light Transmission: Though a minor effect, bubbles can slightly scatter light, preventing it from reaching the cell surface and marginally reducing power output.
What is a multi-step vacuum profile?
Instead of pulling the vacuum from atmospheric pressure down to the final target (e.g., 1 mbar) in one continuous step, a multi-step profile breaks the process into stages. For example, it might pull down to 500 mbar and hold for a minute, then pull to 100 mbar and hold again, before finally pulling down to the ultimate vacuum level. These pauses allow gases to migrate out of the laminate stack in a controlled manner.
Is this issue specific to POE encapsulants?
While this phenomenon is particularly pronounced with fast-curing materials like POE due to their rapid cross-linking, the fundamental principle applies to all encapsulants, including EVA. Any process that traps air or volatiles before they can be evacuated will create voids, regardless of the material used.
The Path to a Perfect Lamination
The pursuit of higher throughput can’t come at the expense of quality. As this analysis shows, a seemingly minor adjustment to the lamination vacuum profile can be the difference between a module that degrades prematurely and one that delivers stable, reliable power for decades.
By understanding the physics of outgassing and thoughtfully validating your process parameters, you can ensure that the performance you designed on paper is the performance your customers get in the field.
Ready to explore how process optimization can enhance your module designs? Dive deeper into the world of applied solar module lamination process validation and discover how to build more reliable products from the ground up.