Perovskite solar cells are the talk of the industry, promising unprecedented efficiency and flexibility. But as manufacturers race to bring these next-generation modules to market, a critical, often-overlooked vulnerability is emerging: the bond between the low-temperature encapsulant and the cell’s surface.
Get this bond wrong, and you are not just looking at a minor defect. You are looking at a ticking time bomb for delamination, moisture ingress, and catastrophic field failure.
The core challenge lies in the perovskites‘ famous sensitivity to heat. The high temperatures used to cure traditional EVA encapsulants can destroy the delicate perovskite layer. This sensitivity has forced the industry to adopt new, low-temperature encapsulants. While these materials protect the cell during manufacturing, their long-term adhesion to the unique Transparent Conductive Oxide (TCO) layers used in perovskite cells remains a critical unknown.
This is where the meticulous work of ensuring durability begins—and where many R&D projects falter.
The Critical Interface: Where Modules Succeed or Fail
Think of a solar module as a multi-layer sandwich. Every layer must stick perfectly to its neighbors for the next 25+ years. For perovskite modules, the most fragile connection is often between the encapsulant and the TCO layer on the cell.
Why is this bond so tricky?
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Unique Surface Chemistry: TCOs used for perovskites (like Indium Tin Oxide, or ITO) have different surface properties than the silicon wafers in traditional cells. Adhesion is not a given.
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Low Curing Temperatures: The gentle curing process required for perovskites means the encapsulant has less thermal energy to form strong, cross-linked chemical bonds with the TCO surface.
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Moisture Sensitivity: Perovskite cells are highly susceptible to moisture. Any weakness in the encapsulant bond can create a pathway for water vapor to penetrate the module, leading to rapid degradation.
A weak bond here is the first domino to fall, leading to delamination. This allows moisture to seep in, which in turn degrades the perovskite cell and causes complete module failure.
Quantifying Durability: The 90° and 180° Peel Test Protocol
You can’t manage what you can’t measure. To understand and prevent adhesion failure, we need a reliable way to quantify the bond strength at this critical interface. The solution is peel strength testing—a highly controlled process that measures the force required to pull the encapsulant away from the TCO layer.
At PVTestLab, we follow a rigorous two-stage protocol not only to measure the initial bond but also to predict its long-term durability.
Stage 1: Initial Bond Strength (Post-Lamination)
The first step is to establish a baseline. We produce a module sample during our lamination process trials, prepare test strips, and measure the initial peel strength.
Using a specialized tensiometer, we pull the encapsulant from the glass/TCO substrate at a constant speed and a precise angle, typically 90° or 180°. Our setup precisely controls these variables to ensure reproducible results, recording the force required in Newtons per centimeter (N/cm).
A good initial bond is essential, but it’s only half the story. The real question is: how will that bond hold up after years of heat, humidity, and thermal cycling in the field?
Stage 2: Durability Assessment (Post-Damp Heat Exposure)
To simulate aging, we subject the laminated samples to an accelerated stress test: Damp Heat (DH) exposure. The industry-standard protocol involves placing the samples in a climatic chamber at 85°C and 85% relative humidity for 1,000 hours.
This harsh environment aggressively challenges the chemical bonds at the encapsulant-TCO interface. It’s the ultimate test of durability.
After the 1,000-hour DH test, we repeat the exact same peel strength measurement. The resulting „after“ value reveals the material’s long-term reliability.
Interpreting the Results: What We Look For
When we analyze the data, we’re looking for two key indicators:
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Absolute Peel Strength: For low-temperature encapsulants, we expect an initial peel strength of at least 8-10 N/cm. Anything lower suggests a poor initial bond.
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Strength Retention: This is the most critical metric. A robust encapsulant should retain over 70% of its initial peel strength after 1,000 hours of damp heat. If we see a drop of 50% or more, it’s a major red flag indicating that the bond will likely fail prematurely in the field.
Expert Insight from Patrick Thoma, PV Process Specialist at PVTestLab:
„We’ve seen new encapsulants that show fantastic initial adhesion, well over 12 N/cm. But after damp heat, the strength plummets to 4 N/cm. This is a classic sign of hydrolysis, where moisture breaks down the chemical bonds. Without this post-DH testing, a developer might unknowingly approve a material combination destined for failure. Quantifying this degradation is fundamental to de-risking new module designs.“
We also analyze the failure mode. Did the bond break cleanly at the TCO interface (adhesive failure), or did the encapsulant itself tear (cohesive failure)? Cohesive failure is often preferred, as it indicates the bond to the TCO is stronger than the encapsulant material itself.
This systematic approach is a core part of effective solar module prototyping, transforming the abstract risk of delamination into a concrete, data-driven decision.
Why This Matters for Your R&D
Ignoring adhesion testing is like building a skyscraper on an untested foundation. For developers of perovskite modules, material suppliers, and research institutions, a proactive approach is crucial.
- Material Manufacturers: Quantify how your new low-temperature encapsulant performs on different TCO surfaces to provide reliable data to your customers.
- Module Developers: Compare encapsulants from different suppliers head-to-head to select the most durable option for your specific cell architecture.
- Research Institutions: Validate whether a new TCO formulation or surface treatment improves long-term encapsulant adhesion before scaling up.
By integrating peel strength testing early in the development cycle, you can avoid costly late-stage failures, accelerate your time-to-market, and build modules with the long-term reliability the industry demands.
Frequently Asked Questions (FAQ)
What is a TCO layer?
TCO stands for Transparent Conductive Oxide. It is a thin, optically transparent film that is also electrically conductive, making it essential for letting light into the solar cell while extracting electrical current. Indium Tin Oxide (ITO) is a common TCO used in perovskite cells.
What is a solar encapsulant?
An encapsulant is a polymer material, typically supplied in sheets, used to laminate solar cells between the glass and backsheet. It provides structural adhesion, electrical insulation, and protection from environmental factors like moisture and oxygen.
Why can’t we just use standard EVA encapsulant for perovskite modules?
Standard Ethylene Vinyl Acetate (EVA) requires lamination temperatures around 145-150°C to properly cure and cross-link. Perovskite solar cells are extremely sensitive to these high temperatures and can be irreversibly damaged or destroyed during the process. This necessitates the use of encapsulants that cure at much lower temperatures, often below 120°C.
What is the difference between a 90° and a 180° peel test?
The angle refers to the direction the encapsulant is pulled relative to the substrate. In a 90° test, the material is pulled perpendicular to the cell surface. In a 180° test, it is folded back on itself and pulled parallel to the surface. The choice depends on the specific standard being followed or the interface being tested, but both provide critical data on bond strength.
How long does a full peel test cycle take?
The initial post-lamination test can be done in a single day. However, the full durability assessment requires the 1,000-hour (approximately 42 days) damp heat exposure period before the final peel test can be conducted.
The First Step to Building a Better Module
Understanding the nuances of encapsulant adhesion is no longer optional—it is fundamental to the success of perovskite solar technology. By moving beyond assumptions and implementing rigorous, quantitative testing, we can unlock the immense potential of these next-generation cells and build modules that are not only highly efficient but also reliably durable.
Ready to move from theory to practice? Explore how applied R&D in a real production environment can validate your materials and designs.