Imagine holding a solar cell with record-breaking potential. It’s efficient, lightweight, and promises to revolutionize the renewable energy landscape. But there’s a catch: it’s incredibly fragile, degrading rapidly when exposed to the open air. This is the central challenge for researchers and engineers working with perovskite solar cells.
The immense promise of perovskite technology is shadowed by its notorious instability. Protecting these sensitive layers from moisture, oxygen, and heat isn’t just a hurdle—it’s the primary barrier standing between laboratory breakthroughs and commercial reality.
Your choice of encapsulant—the protective material sealing the cell from the elements—is one of the most critical decisions you’ll make. Today, two main families of low-temperature materials lead the field: liquid silicones and thermoplastics. So, which one is right for your project?
Why „Low Temperature“ is a Game-Changer for Perovskites
For decades, conventional silicon solar modules have relied on robust encapsulants like EVA (ethylene vinyl acetate), laminated at temperatures around 150°C. This process creates a durable, weatherproof seal that can last for 25 years or more.
Perovskite materials, however, simply cannot take the heat.
Exposing them to temperatures above 130°C causes irreversible degradation, destroying the very efficiency you worked so hard to achieve. This fundamental limitation forces a complete shift in material science, requiring the entire lamination process to be re-engineered for lower temperatures. Specialized encapsulants are a necessity, not an option.
Meet the Contenders: A Tale of Two Materials
While liquid silicones and thermoplastics serve the same purpose, their fundamental chemistry and processing requirements are worlds apart. Understanding these differences is key to making an informed decision.
The Case for Liquid Silicone
Think of liquid silicone as a high-tech, two-part epoxy. It starts as a viscous liquid that is precisely dispensed over the solar cell stack. When heated gently, a chemical reaction—curing—occurs, causing the liquid to cross-link and form a permanent, solid, and flexible rubber integral to the module.
Key Strengths:
- Superior Moisture Barrier: Once cured, its cross-linked structure is extremely effective at blocking water molecules.
- Excellent UV Stability: Silicone is inherently resistant to degradation from sunlight, ensuring long-term optical clarity.
- Thermal Flexibility: It remains stable across a wide range of temperatures without becoming brittle or soft.
The Case for Thermoplastics
Thermoplastic encapsulants, often based on materials like polyisobutylene (PIB), behave more like a high-performance laminating film. Supplied as a solid sheet, the film is placed into the module stack and heated during lamination until it softens and flows around the cells. As it cools, it solidifies, creating a protective layer.
Key Strengths:
- Process Simplicity: It handles like a traditional film, making it easier to integrate into familiar, scalable lamination workflows.
- Faster Cycle Times: With no chemical curing time required, the lamination process can be significantly quicker.
- Cost-Effectiveness: The material and processing often offer a more economical path to large-scale production.
The Head-to-Head Comparison: Insights from PVTestLab Trials
Theory is one thing; performance under industrial conditions is another. Let’s see how these two encapsulant families compare on the critical parameters that determine a perovskite module’s success.
Moisture Barrier Performance (WVTR): The First Line of Defense
For perovskites, the single most important metric is the Water Vapor Transmission Rate (WVTR), which measures how much moisture passes through the material over time.
Our findings from numerous lamination trials are clear: liquid silicones consistently deliver a superior moisture barrier. Their cured, cross-linked structure achieves an extremely low WVTR—often below 10⁻³ g/m²/day—providing maximum protection. And while advanced thermoplastics offer good performance, they typically require a secondary edge sealant (like butyl tape) to prevent moisture from creeping in from the sides over the module’s lifetime.
Processability and Scalability: From Lab to Fab
This is where thermoplastics truly shine. Their film-based format is straightforward to handle and automate. The lamination process is fast and highly repeatable—a major advantage when planning for high-volume manufacturing.
Liquid silicones, however, demand a more complex process. They require specialized dispensing equipment to apply the material evenly without introducing air pockets, and the subsequent curing step adds time to the production cycle. Without precise control, issues like bubbles or inconsistent thickness can compromise the entire module.
Expert Insight from Patrick Thoma, PV Process Specialist at PVTestLab:
„We see clients succeed with both materials, but the choice depends on their stage of development. For maximum protection in early-stage R&D, silicones are hard to beat. But for those planning a pilot line, the process simplicity of thermoplastics is incredibly compelling. The key is validating how the material behaves with your specific module design on industrial equipment.“
Optical Properties and Long-Term Stability
Both material types offer excellent initial optical transmission, ensuring that maximum light reaches the perovskite cell. However, long-term stability is a critical consideration. Silicones have a proven track record of UV resistance, maintaining their clarity for years. Some thermoplastics, if not properly formulated with UV stabilizers, can be susceptible to yellowing or hazing over time, which reduces the module’s energy yield.
Making the Right Choice for Your Project
So, which encapsulant should you choose? The answer depends on your project’s primary goal.
- Choose liquid silicone if: your top priority is achieving the absolute best moisture protection and long-term durability, especially during the R&D phase where performance validation is paramount.
- Choose thermoplastics if: your focus is on process scalability, faster throughput, and a clear path to cost-effective mass production.
Ultimately, the goal is to build reliable prototype solar modules that prove your technology’s viability. Testing your material in a controlled, industrial environment is the only way to truly understand how it will perform.
Frequently Asked Questions (FAQ)
Q1: What is WVTR and why does it matter so much for perovskites?
WVTR stands for Water Vapor Transmission Rate. It measures how easily water vapor can pass through a material. Perovskite crystals are extremely sensitive to moisture, which causes them to rapidly degrade and lose their photovoltaic properties. A low WVTR is the most critical factor in ensuring a long and stable life for the module.
Q2: Can I just use standard EVA encapsulant for my perovskite module?
No. Standard EVA requires lamination temperatures around 150°C, which is far too hot for perovskite cells and will cause immediate and severe damage to their delicate structure.
Q3: What does „curing“ mean for liquid silicone?
Curing is the chemical process where the two liquid components of the silicone react (triggered by heat) to form a solid, stable, cross-linked polymer network. This differs from thermoplastics, which simply melt and re-solidify without a chemical change.
Q4: Does the choice of encapsulant affect the final module efficiency?
Yes, both directly and indirectly. Directly, the encapsulant’s optical transparency determines how much light reaches the cell. Indirectly, and more importantly, its ability to protect the cell from degradation determines how much of that initial efficiency is retained over time. A poor encapsulant will lead to rapid efficiency loss.
Your Path From Material to Module
Choosing between liquid silicone and thermoplastic encapsulants isn’t about finding a single „best“ material, but about aligning your choice with your strategic goals. One offers ultimate protection; the other provides a clearer path to scale.
The most important step is moving beyond datasheets and into the real world. A comprehensive understanding of module encapsulation is built on applied testing. Validating your material on a full-scale production line is the fastest way to de-risk your technology, uncover hidden processing challenges, and accelerate your journey from lab to market.