You’ve invested in the latest high-efficiency TOPCon cells. You’re embracing advanced interconnection technologies like Multi-Busbar (MBB) or shingling to squeeze every last watt out of your solar modules. The datasheets promise record-breaking performance. But after lamination, you’re seeing frustrating results: tiny bubbles near the busbars, subtle voids along the shingled overlaps, or worse, post-test analysis revealing micro-cracks.

Suddenly, that promised efficiency gain feels fragile.

This is an increasingly common story in the solar industry’s rapid evolution. As cell technology leaps forward, supporting manufacturing processes—especially lamination—must adapt with equal precision. The flat, simple landscape of a traditional 5-busbar cell is gone. Today’s modules are complex, three-dimensional structures, and ensuring the encapsulant flows perfectly into every nook and cranny has become both an art and a science.

Why Lamination Isn’t „One Size Fits All“ Anymore

For years, lamination was a relatively standardized process. You placed your cell string, encapsulant, and glass, then applied heat and pressure according to a well-known recipe. But the intricate geometries of MBB and shingled cells have changed the rules.

Think of it this way: perfectly gift-wrapping a simple, flat box is easy. Now, try wrapping a complex sculpture with dozens of fine wires and overlapping edges without a single air bubble or crease. It’s a completely different challenge.

• Multi-Busbar (MBB) Cells: Instead of a few flat ribbons, you now have a dense grid of up to 18 round wires. This creates a forest of tiny obstacles. The encapsulant must flow evenly around every single wire. If it flows too fast or under the wrong pressure, it can trap pockets of air, creating voids that become hot spots later.
• Shingled Cells: Here, cells are overlapped and bonded with electrically conductive adhesive (ECA). This overlap creates a „step“ or a ridge. During lamination, this step can become a high-pressure point, potentially stressing the ultra-thin silicon. It also creates a channel where air can easily get trapped if not evacuated properly.

These new designs mean we can no longer treat the module layup as a simple, two-dimensional plane.

At the heart of this new challenge is the need for perfect, void-free encapsulation. Research shows that voids and bubbles act as insulators, leading to localized overheating (hot spots) that can degrade the cell and encapsulant, causing irreversible power loss. For TOPCon cells, which are particularly sensitive to moisture, a void can become a pathway for humidity ingress, accelerating degradation and compromising the module’s long-term reliability.

The Anatomy of a Failed Lamination

When you’re dealing with the tight tolerances of MBB and shingled TOPCon, several things can go wrong inside the laminator if the process isn’t perfectly tuned.

Trapped Air and Outgassing

Before the encapsulant (like EVA or POE) melts and cross-links, all air must be evacuated from the module layup. The dense wiring of MBB and the overlaps of shingled cells create complex pathways that make this evacuation difficult. Some encapsulants and backsheets can also release small amounts of gas (outgassing) during heating. If pressure is applied too soon, this air and gas gets trapped, forming bubbles. A trapped bubble creates a void—an area with no adhesion between the cell and the glass or backsheet. Studies on PV module reliability show these voids are a primary starting point for delamination, especially under thermal cycling stress. Over time, the void can grow, compromising the module’s structural integrity and exposing the cell to environmental damage.

Non-Uniform Pressure

The „steps“ from shingled cells and the grid of MBB wires mean that when the laminator’s membrane presses down, the pressure isn’t applied uniformly. Some areas, like the cell overlaps, experience much higher mechanical stress. This concentrated pressure can induce micro-cracks, which are often invisible to the naked eye but show up clearly in electroluminescence (EL) testing. These cracks disrupt the flow of electricity, creating inactive cell areas and directly reducing the module’s power output. Successful Prototyping & Module Development hinges on eliminating this very risk.

Mastering the Flow: Fine-Tuning the Lamination Recipe

The solution isn’t to abandon these high-efficiency designs; it’s to evolve the lamination process with a focus on intelligent control of pressure and temperature. The goal is to give the encapsulant time to flow like liquid honey into every tiny space before it cures into a solid, protective layer.

1. Pressure is More Than Just a Number: The Multi-Stage Approach

Instead of a single, high-pressure application, a multi-stage pressure profile is far more effective.

• Stage 1: Low-Pressure „Dwell“ Time: After the initial vacuum, the process holds at a very low pressure while the temperature rises. This allows the encapsulant to soften and slowly seep into the gaps around wires and overlaps, pushing out any residual air before it can get trapped.
• Stage 2: Gradual Pressure Ramp: The pressure is then increased slowly. This gentle squeeze helps the encapsulant flow without creating high-stress points.
• Stage 3: Full Pressure for Curing: Only when the encapsulant has fully melted and filled all voids is the final, high pressure applied to ensure strong adhesion and complete cross-linking.

2. The Temperature Dance: Controlling Viscosity

The viscosity (or thickness) of the encapsulant is controlled by temperature, making a proper temperature ramp critical. If you heat too quickly, the encapsulant can start to cure (cross-link) before it has finished flowing—a common cause of voids. A slower, more controlled temperature ramp keeps the encapsulant in its low-viscosity, liquid-like state for longer, giving it the time needed to navigate the complex topography of an MBB or shingled cell layout.

This careful choreography of pressure and temperature is what ensures a perfect, uniform encapsulation.

3. Material Synergy Matters

The choice of encapsulant is also critical. POE, for example, often has different flow characteristics and is less prone to outgassing than some traditional EVA formulations, making it a strong candidate for sensitive TOPCon cells. However, it also requires its own unique lamination recipe. Running structured Material Testing & Lamination Trials is the only way to confirm which material and process combination delivers the best results for your specific module design.

From Theory to Factory Reality

Developing these advanced lamination recipes requires more than just theory. It demands an environment where you can test, measure, and refine your process under real industrial conditions. Every combination of cell, encapsulant, and backsheet behaves differently. What separates market-leading modules from the rest is the ability to build prototypes, adjust parameters on a full-scale laminator, and immediately analyze the results with EL and sun simulation.

As solar technology continues to push the boundaries of efficiency, the manufacturers who succeed will be the ones who master not just the cells themselves, but the intricate processes that turn those cells into reliable, high-performance solar modules.

Frequently Asked Questions (FAQ)

What exactly is a lamination void?

A lamination void is a pocket of air or gas trapped within the module layup, most commonly between the encapsulant and a cell, or between the encapsulant and the glass or backsheet. It represents a failure of adhesion and can lead to hot spots and long-term degradation.

Why is POE often recommended for TOPCon cells?

TOPCon cells have a passivated contact layer that is sensitive to the acetic acid byproducts generated by EVA encapsulants during curing and aging. POE (Polyolefin Elastomer) does not produce acetic acid, making it a more chemically compatible choice that helps preserve the cell’s long-term efficiency and prevent potential-induced degradation (PID).

Can I use my standard lamination recipe for MBB cells?

It’s highly discouraged. A standard recipe is typically not optimized for the complex topography of MBB cells. It often leads to air entrapment around the dense wires, resulting in voids. A specific, multi-stage pressure and temperature profile is needed to ensure complete encapsulation.

What’s the difference between a micro-crack and a void?

A void is a lack of material (an air bubble), while a micro-crack is a physical fracture in the silicon cell itself. Voids are typically caused by process issues during lamination (poor flow, trapped air), whereas micro-cracks are caused by mechanical stress, which can occur during stringing, handling, or lamination if the pressure is non-uniform.

How does shingling increase mechanical stress during lamination?

The overlapping of shingled cells creates a „step-up“ in thickness. When the flat membrane of the laminator presses down, this step concentrates the force on a very small area, creating a high-pressure point that can induce stress and micro-cracks in the thin silicon wafers if not managed with a carefully controlled lamination recipe.