Modern solar manufacturing faces a great paradox. We’ve engineered next-generation cells like TOPCon and HJT that are more efficient than ever, pushing the boundaries of power output. Yet in the race for higher performance, we’ve also made them incredibly delicate. This hidden fragility creates a new and critical challenge on the production line—one that often goes unnoticed until it’s too late.
The culprit? Microcracks. These tiny, invisible fractures can slash a module’s output and compromise its long-term reliability. The shocking part is, they are often created during the one process designed to protect the cells: lamination.
The New Generation of Solar Cells: A Double-Edged Sword
To understand the problem, it helps to know what makes TOPCon (Tunnel Oxide Passivated Contact) and HJT (Heterojunction) cells so special. Their advanced multi-layer structures are masterpieces of engineering, allowing them to capture more sunlight and convert it into electricity with unprecedented efficiency.
But this performance comes at a cost.
A typical PERC cell is around 160 micrometers (µm) thick. In contrast, many TOPCon and HJT cells are now just 120–130 µm thick—nearly 25% thinner. This makes them incredibly susceptible to mechanical stress. While they may look robust, they require a new level of precision during handling.
This fragility isn’t just a handling issue; it fundamentally changes the rules of module assembly. The immense pressure of lamination, once considered standard procedure, has become a primary source of cell damage and yield loss.
The Hidden Danger in Traditional Lamination
For years, the lamination process was a straightforward affair: assemble the module sandwich (glass, encapsulant, cells, encapsulant, backsheet), place it in a laminator, and apply uniform heat and pressure. This single, high-pressure event forces the encapsulant—materials like EVA or POE—to melt and bond everything together.
For thicker, more robust cells, this worked perfectly.
With ultra-thin TOPCon and HJT cells, however, this „one-shot“ pressure application is like hitting a porcelain plate with a hammer. When nearly one bar of pressure is applied instantly, the encapsulant liquefies and flows rapidly, creating powerful hydrodynamic forces that push, pull, and flex the delicate cells. Unable to withstand the stress, they develop microcracks.
These cracks are often invisible to the naked eye but show up clearly on an electroluminescence (EL) test. They appear as dark, inactive areas that cripple a module’s performance—the silent yield killer, introducing defects at the final stage of production.
A Smarter Approach: Multi-Stage Pressure Control
If sudden, high pressure is the problem, the solution is a more intelligent, gradual approach. This is the principle behind multi-stage pressure control, a technique that transforms lamination from a brute-force event into a carefully orchestrated process.
Instead of applying full pressure at once, the process is broken into distinct stages, giving the materials time to settle and bond without inducing stress.
Here’s how it works in practice:
Stage 1: The Gentle Melt (Low Pressure)
The cycle begins with a low-pressure phase, typically around 0.1 to 0.2 bar. This is just enough pressure to hold the module sandwich together as the encapsulant slowly melts and softens. It flows gently around the cells, filling every gap without exerting significant force. Think of it as pouring cream into coffee, allowing it to mix gently rather than splashing it in all at once.
Stage 2: The Conforming Squeeze (Medium Pressure)
Once the encapsulant is fully molten and has settled, the pressure increases to a medium level, around 0.5 to 0.8 bar. At this stage, the liquid encapsulant is pressed firmly into place, ensuring complete material conformity and removing any trapped air bubbles. Because the cells are already embedded in the soft encapsulant, they are cushioned from the pressure increase, which prevents mechanical stress.
Stage 3: The Final Bond (High Pressure)
Only in the final stage is the full pressure of approximately 1.0 bar applied. This step ensures a permanent, void-free bond and initiates the cross-linking (curing) that gives the module its structural integrity. By this point, the cells are fully supported and immobile within the encapsulant matrix, protecting them from the high pressure.
„The physics are clear,“ notes Patrick Thoma, a PV Process Specialist at PVTestLab. „You cannot treat a 120-micron HJT cell the same way you treat a 160-micron PERC cell. The key is to manage the flow dynamics of the encapsulant. By staging the pressure, we allow the encapsulant to become a protective cushion before we apply the force needed for bonding. It’s a fundamental shift in how we think about optimizing the lamination process.“
The Proof is in the Process: Data from the Lab
Does this careful, staged approach actually make a difference? The data is conclusive.
In a series of controlled trials at PVTestLab, we compared modules made with traditional single-stage lamination against those made with a multi-stage pressure profile. Using identical TOPCon cells and encapsulant materials, the results were dramatic. Modules produced with multi-stage pressure control showed up to an 85% reduction in microcrack formation.
This directly translated into higher, more consistent production yields, with an average power output improvement of 2–3%. That’s a massive gain in an industry where every fraction of a watt counts. These findings underscore just how important it is to align process parameters with material properties. For anyone developing new solar modules, this means proper process validation and advanced material testing are critical to perfecting the recipe.
Frequently Asked Questions (FAQ)
What exactly is a solar cell microcrack?
A microcrack is a tiny, often microscopic fissure in the silicon wafer of a solar cell. While sometimes caused by handling, they are frequently induced by thermal or mechanical stress during manufacturing. These cracks disrupt the flow of electrons, reducing a cell’s efficiency and creating hotspots that can lead to long-term module failure.
Are all TOPCon and HJT cells more fragile?
Generally, yes. The trend toward thinner wafers—to reduce silicon consumption and improve certain electrical properties—makes them inherently more susceptible to mechanical stress than their thicker PERC predecessors.
Does this multi-stage process take longer?
The total lamination time can be slightly longer, but the increase is often negligible compared to the significant gains in yield and reliability. A properly optimized cycle adds very little time while preventing costly rejects.
Can this method be applied to my existing production line?
In many cases, yes. Most modern industrial laminators are programmable and can be configured with multi-stage pressure and temperature profiles. It’s less about new hardware and more about developing the right process recipe for your specific combination of cells, encapsulants, and module design.
From Theory to Factory Floor
The transition to higher-efficiency cell technologies like TOPCon and HJT is an incredible leap forward for the solar industry. But to fully capitalize on their potential, we must adapt our manufacturing processes to respect their delicate nature.
Rethinking lamination is no longer optional—it’s essential. By moving away from outdated, brute-force methods and embracing intelligent, multi-stage pressure control, manufacturers can protect their investment in next-generation cells, reduce defects, and unlock the full performance of their modules.
If you’re navigating the complexities of new module designs or facing unexplained yield loss, a deeper look at your lamination dynamics is the most critical first step. Understanding and controlling these forces is the key to building the powerful, reliable solar modules of the future.