Imagine your team has just developed a cutting-edge Heterojunction (HJT) solar module. The initial flash tests are incredible, with efficiency numbers that leave standard technologies in the dust. The future looks bright.
But what happens after a thousand days in the humid heat of Florida, or five thousand days of freeze-thaw cycles in the German Alps? Suddenly, that world-beating efficiency means little if the module itself is falling apart.
This is the hidden threat facing many HJT innovators. The very heat sensitivity that makes HJT cells so efficient also forces a manufacturing compromise that can lead to catastrophic failure down the line: poor adhesion. And the only way to know if you’re at risk is to break things on purpose.
The HJT Lamination Challenge: A Delicate Balancing Act
To understand the problem, think of laminating a solar module like baking. Most conventional solar cells are robust. You can „bake“ them at high temperatures (around 165°C or higher) to ensure the encapsulant—the „glue“ holding everything together—cures into a tough, weatherproof barrier. This process, known as cross-linking, forges the powerful chemical bonds that give a module its strength.
HJT cells are different; they’re more like a delicate soufflé.
Their high-performance Transparent Conductive Oxide (TCO) layers are extremely sensitive to heat. Exposing them to temperatures above 165°C can degrade their electrical properties, erasing your efficiency gains.
This forces manufacturers into a corner: they must use a low-temperature lamination process. Lowering the heat, however, starves the encapsulant (like POE or EVA) of the energy it needs to fully cross-link. The result is a weaker initial bond between the encapsulant, the cell, and the glass. A module might look perfect coming off the line, but it carries a hidden weakness.
The Real Test Isn’t Day One—It’s Year Twenty
A brand-new module in a lab says little about its ability to survive two decades of harsh weather. Out in the real world, modules face a constant barrage of heat, humidity, UV radiation, and mechanical stress.
To simulate this lifetime of abuse, the solar industry uses accelerated aging tests in a climate chamber. The most telling of these is the Damp Heat (DH) test, which subjects a module to a punishing environment of 85°C and 85% relative humidity for 1,000 hours.
This test is where the compromise of low-temp lamination comes back to haunt you. Inside the module, tiny water vapor molecules work their way into the layers. Combined with high heat, this moisture attacks the already-tenuous bonds between the encapsulant and the cell or glass. For certain encapsulants like EVA, this can also create acetic acid, further accelerating degradation. What started as a microscopic failure in adhesion begins to spread, causing the layers to separate.
Once delamination starts, it opens up pathways for more moisture, leading to corrosion, short circuits, and a rapid decline in power output. The module that tested perfectly on day one begins to fail prematurely in the field.
Measuring What Matters: The Post-Stress Peel Strength Test
How can you predict this failure before it happens? You can’t just look at a module; you need to quantify the bond strength after it has been aged.
This is the purpose of the peel strength test, standardized under IEC 62788-1-4. After a module sample endures the full Damp Heat test, a strip of the encapsulant and backsheet is carefully cut and pulled off the solar cell at a controlled speed and angle.
A force gauge measures the exact strength, in Newtons per centimeter (N/cm), required to separate the layers. This isn’t a subjective assessment—it’s hard data that reveals the true integrity of the lamination.
In the industry, a peel strength of greater than 40 N/cm is widely considered the benchmark for a robust, long-lasting bond. Anything less signals a high risk of field delamination. This single number can be the difference between a reliable 25-year product and a costly warranty nightmare.
How to De-Risk Your HJT Module Design
The challenge for HJT module developers isn’t just achieving high efficiency; it’s proving that this efficiency can be sustained for decades. Avoiding delamination requires a methodical, data-driven approach to the lamination process.
The goal is to find the „sweet spot“—a process that cures the encapsulant enough to form a durable, weather-resistant bond without damaging the sensitive HJT cells. Finding that sweet spot involves systematically testing and validating several key variables:
- Encapsulant Selection: Testing different formulations of low-temperature POE or other specialized encapsulants is the first step.
- Process Parameters: Fine-tuning the temperature profile, pressure, and curing time can dramatically impact cross-linking and adhesion.
- Module Construction: The type of glass, backsheet, and cell texturing can all influence how well the encapsulant adheres.
Developing new [solar module concepts] with HJT technology requires moving beyond datasheets and simulations. It demands building physical prototypes, subjecting them to realistic stress, and measuring the outcomes. A deep understanding of [lamination process parameters] is essential to creating a product that is both high-performing and durable.
Only by combining these elements can you create a process recipe that is truly optimized—not just for Day 1 efficiency, but for Year 25 reliability.
Your Questions on HJT Adhesion, Answered
What is delamination and why is it so bad?
Delamination is the physical separation of the layers within a solar module, such as the encapsulant pulling away from the glass or the solar cell. It’s a critical failure because it breaks the module’s protective seal, allowing moisture and oxygen to enter. This leads to corrosion, electrical failures, and significant power loss long before the module’s expected lifetime is over.
Can’t you just use a stronger glue?
The encapsulant in a solar module does much more than act as a simple glue. It must remain optically transparent for decades, provide electrical insulation, and be flexible enough to handle thermal expansion and contraction. Sophisticated polymers like POE and EVA are designed for this purpose, but their bonding performance is directly tied to the lamination process—heat, time, and pressure. The solution isn’t a different „glue,“ but a precisely optimized process for the right material.
Is this test only for HJT modules?
While peel testing after climate chamber exposure is especially critical for temperature-sensitive HJT modules, it is a valuable validation tool for any PV module technology. Any change in materials—a new backsheet, a different encapsulant, or a new cell coating—can affect adhesion. Verifying peel strength is a fundamental part of de-risking any new module design.
Don’t Let Adhesion Be Your Achilles‘ Heel
The pursuit of higher efficiency with HJT technology is pushing the solar industry forward, but this innovation brings new manufacturing challenges that cannot be ignored. A weak bond from a low-temperature lamination process can silently undermine the entire value of a high-performance module.
Initial power output is only half the story. True quality and bankability are proven by durability. By integrating post-damp-heat peel strength testing into your development cycle, you move from hoping your modules will last to knowing they will.
Understanding these potential failure modes is the first step toward building truly reliable and innovative solar products. If you are navigating the complexities of new materials or processes, creating a robust validation plan is the most important investment you can make. Don’t leave durability to chance—[talk to a process specialist] to build a test plan that ensures your modules last.