The most effective encapsulation techniques for perovskite solar cells (PSCs) focus on protecting the sensitive perovskite layer from moisture, oxygen, UV light, and mechanical damage to enhance their long-term stability and operational lifetime. Based on recent research and reviews, the following encapsulation methods have proven particularly effective:
1. Glass-Glass Encapsulation
- This technique sandwiches the PSC between two glass layers, providing a robust physical barrier against moisture and oxygen ingress.
- Glass-glass encapsulation also offers excellent mechanical protection and durability suitable for outdoor application.
- It is one of the most reliable and widely used commercial encapsulation methods, achieving extended outdoor operational stability when combined with lamination and edge sealing techniques.
2. Polymer Thin-Film Encapsulation
- Various polymers have been used as thin encapsulation films directly on PSCs, including PMMA (poly(methylmethacrylate)), PDMS (polydimethylsiloxane), parylene C, thermoplastic polyurethane (TPU), fluoropolymers, and combinations like PMMA with silicone rubber or styrene-butadiene.
- These polymer films typically offer good optical transparency and flexibility, allowing for lightweight and flexible device designs.
- TPU stands out for its optical transparency, mechanical flexibility, and effectiveness in protecting inorganic PSCs.
- Some polymers are enhanced by adding hydrophobic or barrier-improving coatings such as H-perfluorodecyltrichlorosilane, which increases moisture resistance.
3. Inorganic Thin-Film Barriers
- Atomic Layer Deposition (ALD), e-beam evaporation, RF sputtering, and plasma-enhanced chemical vapor deposition (PECVD) are used to deposit thin inorganic films (e.g., zirconia, aluminum oxide) that act as impermeable barriers to moisture and oxygen.
- Inorganic films are often combined with polymers to form hybrid encapsulation layers that take advantage of the flexibility of polymers and the superior barrier properties of inorganic layers.
4. Graphene and 2D Material Layers
- Roll-transferred graphene and spray-coated reduced graphene oxide (rGO) have been explored as ultra-thin, transparent, and effective encapsulation layers.
- Hexagonal boron nitride (hBN) flakes and polycarbonate have also been tested as encapsulation materials, although these are less common.
5. Facile and Hybrid Methods
- Some approaches utilize conductive ribbons and polyethylene terephthalate (PET) backsheets on both sides of the PSC, combining electrical conductivity with encapsulation protection.
- Glass-coated polymer films combining the advantageous properties of both materials have shown exceptional transparency and barrier properties, offering promising alternatives.
Summary Table of Effective Encapsulation Materials and Techniques
| Encapsulation Type | Materials/Methods | Advantages | Application Notes |
|---|---|---|---|
| Glass-Glass Encapsulation | Laminated glass sheets with edge sealing | Excellent moisture and oxygen barrier, robust | Suitable for outdoor and commercial use |
| Polymer Thin Films | PMMA, PDMS, TPU, parylene C, fluoropolymers | Flexible, transparent, easy to process | TPU noted for flexibility and transparency |
| Inorganic Thin-Film Barriers | ALD Al2O3, e-beam zirconia, RF sputtered films | Superior barrier properties against moisture | Often combined with polymers for hybrid encapsulation |
| Graphene & 2D Materials | Graphene, reduced graphene oxide, hBN flakes | Ultra-thin, transparent, excellent barrier | Less commonly used, emerging technology |
| Hybrid & Facile Approaches | Conductive ribbons + PET backsheets, glass-coated polymers | Combines mechanical, electrical, and barrier properties | Promising for scalable, cost-effective encapsulation |
In conclusion, the most effective encapsulation for perovskite solar cells involves a combination of glass-glass encapsulation for robust protection and polymer/inorganic thin-film layers for flexibility and enhanced barrier performance. TPU polymers, ALD-deposited inorganic films, and hybrid glass-polymer composites currently represent the state-of-the-art in protecting PSCs against environmental degradation and extending their operational lifetimes.
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