The rapid shift from PERC to advanced module technologies like Bifacial, TOPCon, and HJT marks a monumental leap in efficiency. But with this progress comes a new landscape of risk. The familiar degradation mechanisms of PERC are no longer the full story. Relying on standard IEC certifications alone is like navigating a new city with an old map—you’ll miss the critical turns that determine long-term bankability.
For project developers, material suppliers, and module manufacturers, the central question has changed. It’s no longer just „Is it certified?“ but „How will this specific N-type architecture perform after 20 years in the field?“ Answering this question requires a deeper validation approach, one that moves from the laboratory into a real-world production environment.
At PVTestLab, we bridge that gap. We don’t just test modules; we simulate their entire lifecycle under industrial conditions to uncover the subtle, technology-specific failure modes that standard tests miss. This guide breaks down the unique reliability challenges of today’s most promising technologies and outlines a practical framework for ensuring their long-term performance and financial viability.
Bifacial Modules: The Dual-Sided Durability Challenge
Bifacial technology captures light from both sides of the module, boosting energy yield. However, this dual exposure introduces unique stress factors that single-sided testing protocols often overlook.
Unique Reliability Risks
A primary concern for bifacial modules is their increased susceptibility to Potential Induced Degradation (PID) on the rear side. With a transparent backsheet or glass-glass construction, the rear cells are exposed to the same electrical potential stresses as the front, effectively doubling the risk profile. The choice of encapsulant also becomes more critical, as it must maintain transparency and adhesion on both sides, even under prolonged UV and environmental stress.
PVTestLab’s Specialized Validation Process
Our approach goes beyond standard PID testing. In our climate-controlled chambers, we subject bifacial modules to a dual-sided stress sequence that simulates how voltage potential affects both surfaces in the field.
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Bifacial PID Simulation: Our tests are configured to stress front and rear cells simultaneously, replicating a high-voltage string in a field environment.
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Encapsulant & Backsheet Delamination Analysis: We use extended Damp Heat (DH) and Thermal Cycling (TC) tests to analyze the bonding integrity of the entire module sandwich. Afterward, electroluminescence (EL) imaging and visual inspections pinpoint early signs of delamination or moisture ingress that could compromise long-term output.
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LeTID Screening: Because Light and elevated Temperature Induced Degradation (LeTID) can be a significant factor, we conduct extended light-soaking tests at controlled temperatures. This process quantifies and stabilizes the effect for more accurate performance modeling.
Mitigation and Design Recommendations
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Material Selection is Key: For glass-glass bifacial modules, using Polyolefin Elastomer (POE) encapsulants is highly recommended over traditional EVA. POE offers superior resistance to moisture ingress and a much lower water vapor transmission rate (WVTR), providing robust, long-term protection against PID.
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Frame & Junction Box Sealing: Meticulous attention to the quality of edge seals is crucial. Any pathway for moisture can accelerate degradation, making a robust sealing strategy non-negotiable for a bankable bifacial design. You can evaluate various materials through our dedicated Material Testing & Lamination Trials.
TOPCon: Unlocking Efficiency, Managing New Sensitivities
TOPCon (Tunnel Oxide Passivated Contact) technology is rapidly becoming the successor to PERC, thanks to its higher efficiency and lower temperature coefficient. However, the delicate tunnel oxide layer and different doping profile introduce new degradation pathways that require highly specific testing.
Unique Reliability Risks
While N-type cells like TOPCon are inherently resistant to traditional PID-s (shunting), they are vulnerable to a different mechanism known as PID-p (polarization). This effect can cause a recoverable yet significant power loss. More critically, TOPCon cells are highly sensitive to sodium contamination from the module’s front glass. Under damp heat conditions, this sodium can corrode the cell metallization and lead to irreversible power loss.
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PID-p (Polarization): A surface polarization effect that temporarily reduces cell efficiency.
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Sodium Contamination: Sodium ions migrating from the glass can attack the cell’s sensitive layers, especially under high humidity and temperature.
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UV-Induced Degradation (UVID): Certain TOPCon designs can be susceptible to power loss after initial UV exposure, a factor often missed by standard tests.
PVTestLab’s Specialized Validation Process
Validating a TOPCon module means hunting for failure modes that PERC tests were never designed to find. Our process is built to provoke, detect, and quantify these emerging risks.
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Modified Damp Heat Testing: We extend the duration and severity of DH testing (to 2000 hours, for example) to accelerate potential sodium-related corrosion. High-resolution EL imaging before and after the test reveals tell-tale signs of degradation like cell-edge darkening.
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UV Preconditioning & PID Sequence: Before PID tests, we expose modules to a significant UV dosage to uncover any UVID susceptibility, ensuring we test the module in its stable, post-degradation state.
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Process Verification: A module’s reliability is often determined on the manufacturing line. We help clients validate processes like Laser-Assisted Firing (LAF), which research shows can dramatically improve damp heat resistance. By building prototypes with different parameters in our Prototyping & Module Development line, we can isolate the impact of specific production steps.
Mitigation and Design Recommendations
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Mandate POE Encapsulants: For TOPCon modules, POE is not just a recommendation; it’s essential for bankability. Its low acidity and excellent moisture barrier properties are critical for protecting the sensitive cell from both PID-p and sodium-induced corrosion.
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Specify Low-Sodium Glass: Work with glass suppliers to source materials with low sodium content. Verifying this through a structured bill of materials (BOM) test is a crucial due diligence step.
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Confirm Advanced Manufacturing: Ensure your supplier uses modern manufacturing techniques proven to enhance TOPCon durability. The performance difference between a well-made and a poorly made TOPCon module can be stark.
HJT: The High-Performance Path and Its Unique Stresses
Heterojunction (HJT) technology promises some of the highest efficiencies and best temperature performance on the market. It achieves this with a complex structure of amorphous silicon layers sandwiching a crystalline silicon wafer. This complexity, however, places unique demands on the materials and processes used for assembly.
Unique Reliability Risks
HJT cells are extremely sensitive to high temperatures. The low-temperature processes required to manufacture the cells mean that subsequent high-temperature soldering and lamination steps can induce stress or damage the delicate passivation layers.
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TCO Layer Degradation: The Transparent Conductive Oxide (TCO) layers essential for current collection can be degraded by moisture ingress, leading to a drop in fill factor and overall power.
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Busbar & Interconnection Integrity: Low-temperature conductive adhesives are often used instead of traditional solder. The long-term reliability of these connections under thermal cycling stress is a major reliability concern.
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Damp Heat Sensitivity: Like TOPCon, HJT modules can be highly susceptible to power loss in damp heat conditions if the wrong encapsulant or a weak edge seal is used.
PVTestLab’s Specialized Validation Process
Our HJT validation protocol targets the module’s most vulnerable points: material interfaces and interconnections. We use a combination of extended stress tests and advanced characterization to confirm the stability of the entire system.
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Low-Temp Process Simulation: We work with clients to refine lamination recipes in our Process Optimization & Training program before they even build prototypes. Our full-scale production line allows us to test and validate low-temperature cure cycles that protect HJT cells without compromising encapsulant adhesion.
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Extended Thermal Cycling: We subject HJT modules to more aggressive thermal cycling profiles (e.g., -40°C to 85°C for 400 or 600 cycles) to test the mechanical stability of the low-temperature interconnects.
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Component-Level Analysis: We go beyond module-level testing by analyzing the specific bill of materials. This process includes testing the moisture resistance of different conductive adhesives and the stability of various TCO coatings.
Mitigation and Design Recommendations
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Encapsulant is Critical: High-performance POE encapsulants are again the preferred choice. Their inherent moisture resistance is the first line of defense for the sensitive TCO layers.
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Smart Interconnection Strategy: The design and application of conductive adhesives or specialized low-temperature solders must be flawless. Any inconsistency can create a hotspot or point of failure down the line.
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Thorough Production Audits: Given the sensitivity of HJT manufacturing, validating the quality control and process stability of a chosen supplier is just as important as testing the final product.
Frequently Asked Questions
Why aren’t standard IEC 61215 certifications enough for these new technologies?
Standard IEC tests are an excellent baseline for safety and initial quality, but they were designed around the known failure modes of older technologies like PERC. They are often not long or harsh enough to provoke the unique, slower-developing degradation mechanisms seen in TOPCon (sodium corrosion) or HJT (TCO degradation). Bankability requires confidence over a 25+ year lifetime, which demands testing that goes beyond certification minimums.
How does PVTestLab’s approach differ from large-scale testing reports like PVEL’s Scorecard?
PVEL and RETC provide an invaluable service by creating a comparative ranking of mass-produced commercial modules. Our role is different and often complementary. PVTestLab is an applied R&D facility. We work with material suppliers and module developers before mass production to test new materials, optimize a specific bill of materials, and fine-tune manufacturing processes. We help answer why a module performs a certain way and how to improve it, providing the deep process data needed to design a reliable product from the ground up.
Can you test our specific combination of cells, encapsulants, and backsheets?
Yes, this is the core of our service. Our entire facility can be rented, allowing you to bring your materials and work alongside our German process engineers to build and test prototypes using your exact bill of materials. This provides definitive, data-backed answers about how your chosen components will perform together under real industrial conditions, dramatically reducing the risk of a costly field failure.
What is the single most important factor for ensuring the reliability of N-type (TOPCon & HJT) modules?
Based on thousands of hours of testing, the single most impactful choice is the encapsulant. While cell quality and manufacturing processes are vital, selecting a high-quality POE encapsulant over a standard EVA provides a powerful defense against the primary degradation risks for N-type technologies—moisture ingress and PID. It is the foundation of a bankable module design.
De-Risk Your Technology Roadmap
Investing in next-generation PV technology without a validation strategy tailored to its unique risks is a gamble. The only way to ensure long-term performance and bankability is to replace assumptions with empirical data from real-world testing.
Whether you are developing a new module, qualifying a new material supplier, or optimizing your production line, our facility provides the industrial-scale environment and deep process expertise you need.
Contact us to discuss your project. Let’s work together to build the next generation of reliable, high-performance solar modules.