You’ve invested in the future. Pallets of brand-new, high-efficiency TOPCon or HJT cells have arrived, promising record-breaking module power and a significant competitive edge. Your production line is ready. But as the ramp-up begins, a worrying trend emerges: lower-than-expected yields, subtle defects in electroluminescence (EL) tests, and inconsistent performance.
What’s going on?
This is the new reality of solar module manufacturing. The transition from traditional PERC cells to next-generation TOPCon (Tunnel Oxide Passivated Contact) and HJT (Heterojunction) technologies isn’t just an upgrade—it’s a fundamental shift in process engineering. These advanced cells are the high-performance engines of the solar world, but they are also far more sensitive than their predecessors.
Why Your Old PERC Process Is a Recipe for Failure
For years, the industry perfected the lamination process for PERC cells. They were robust, forgiving, and could handle a wide range of temperatures and pressures. Think of them as sturdy wooden building blocks.
TOPCon and HJT cells, however, are more like intricate glass sculptures—incredibly powerful, but demanding a much gentler, more precise approach. This delicacy stems directly from their advanced architecture and materials.
Key Sensitivities of Next-Gen Cells:
- Thermal Stress (HJT): HJT cells use thin layers of amorphous silicon for passivation. If the lamination temperature exceeds ~180°C, these critical layers can degrade, permanently damaging the cell’s efficiency. This demands specialized low-temperature encapsulants and interconnection materials.
- Mechanical Stress (TOPCon & HJT): To boost efficiency and reduce costs, these cells are becoming increasingly thin—often just 120-130 micrometers—which makes them highly susceptible to mechanical pressure during layup and lamination. The delicate polysilicon layer in TOPCon cells is particularly vulnerable to excessive or uneven pressure, which can cause defects.
- New Interconnection Demands: Multi-busbar (MBB) and zero-gap stringing technologies, while boosting performance, introduce more complex stress points across the cell surface.
Trying to force these delicate cells through a process designed for robust PERC cells is like trying to fit a square peg in a round hole. The result is often process-induced damage that silently kills your yield and long-term module reliability.
The Hidden Yield Killers: Micro-Cracks and Other Defects
When a lamination process isn’t optimized for TOPCon or HJT cells, the thermal and mechanical stress doesn’t always result in a visibly shattered cell. Instead, it creates a far more insidious problem: micro-cracks.
These are tiny, often invisible fissures in the silicon that act like dead ends for the flow of electrons. A module filled with micro-cracks will suffer from:
- Lower Power Output: Inactive cell areas reduce the module’s overall wattage.
- Hotspot Formation: Electrical current can concentrate around these cracks, creating hotspots that degrade surrounding materials and pose a long-term safety risk.
- Reduced Reliability: Over time, thermal cycling in the field can cause these small cracks to grow, leading to a faster decline in performance and potential warranty claims.
Patrick Thoma, a PV Process Specialist at PVTestLab, puts it this way: „With TOPCon and HJT, the lamination process transforms from a simple bonding step into a delicate thermal treatment. Every degree and every millibar of pressure matters. Guesswork is the fastest way to turn high-efficiency cells into scrap.“
[An electroluminescence (EL) image showing micro-cracks in a solar cell]
A Data-Driven Path to Success: The 3 Pillars of Process Validation
So, how do you ramp up a new TOPCon or HJT production line without breaking the bank (and your cells)? The answer lies in a proactive, systematic process validation strategy before you hit „start“ on mass production. It’s about testing, not guessing.
Pillar 1: Start with Material Compatibility
The foundation of a stable process is choosing materials that are fully compatible with your specific cell technology. You can’t simply use the same EVA encapsulant you used for PERC.
For HJT, this means sourcing and testing low-temperature cure encapsulants (like POE) and special low-temperature solders for interconnection. For TOPCon, you need to ensure your encapsulant’s chemical composition and shrinkage behavior don’t create undue stress on the cell surface during lamination. A structured material validation program is the only way to confirm these materials will perform reliably under real-world conditions.
Pillar 2: Dial-In Your Lamination „Recipe“
A lamination process is defined by three key variables: temperature, pressure, and time. Finding the perfect balance for your specific combination of cell, encapsulant, and backsheet is critical.
This requires a series of controlled experiments to define the optimal process window. This isn’t theoretical work done on a spreadsheet; it demands hands-on lamination process optimization using industrial-scale equipment. The goal is to find the recipe that ensures perfect bonding and curing without inducing damaging stress on the cells.
Pillar 3: Validate with Real Prototypes
Once you have a promising recipe, the final step is to validate it by building and testing actual modules. This phase of prototyping and small-scale production is your final quality gate before committing to a full-scale ramp-up.
By producing a small batch of modules, you can perform comprehensive quality checks—including flasher tests for power output and high-resolution EL imaging to hunt for any hidden micro-cracks. This data provides the concrete proof you need that your process is stable, repeatable, and ready for the factory floor. Investing in this validation step de-risks your entire ramp-up, saving you immense costs in wasted materials and lost time down the line.
Frequently Asked Questions (FAQ)
What are TOPCon and HJT cells?
TOPCon and HJT are next-generation solar cell technologies that offer higher conversion efficiencies than the more traditional PERC (Passivated Emitter and Rear Cell) technology. They achieve this through more complex structures and sensitive passivation layers.
Why can’t I just use my old PERC process for these new cells?
PERC cells are thicker and more tolerant of high temperatures and mechanical pressure. TOPCon and HJT cells, especially HJT, have delicate layers that can be permanently damaged by the heat and pressure of a standard PERC lamination process. The result is significant efficiency loss and physical defects like micro-cracks.
What is a micro-crack and why is it so bad for a solar module?
A micro-crack is a very small fracture in the silicon wafer of a solar cell. While often invisible to the naked eye, it disrupts the flow of electricity, creating „dead“ areas in the cell. This lowers the module’s total power output and can lead to hotspots, which degrade the module faster and can be a safety concern.
What’s the first step to developing a new process for TOPCon or HJT?
The first step is always to understand your materials. Before you even turn on a laminator, you should conduct a thorough evaluation of encapsulants, backsheets, and interconnection ribbons to ensure they are chemically and physically compatible with the specific cell technology you are using.
Don’t Learn the Hard Way
The move to TOPCon and HJT technology represents a massive leap forward for the solar industry. But with greater performance comes the need for greater process precision. A data-driven validation strategy is how you navigate the challenges of these sensitive cells and unlock their full potential.
Instead of facing a painful and expensive trial-and-error ramp-up, you can build a stable, high-yield manufacturing process from day one. The key is to treat process development not as an afterthought, but as the most critical step on your path to producing next-generation solar modules.