What role do encapsulation techniques play in enhancing the stability of perovskite-silicon tandem solar cells

Encapsulation techniques play a crucial role in enhancing the stability of perovskite-silicon tandem solar cells by protecting the sensitive perovskite layers from environmental and operational degradation factors. These methods address key challenges related to moisture, oxygen ingress, thermal and mechanical stresses, and ion migration, all of which can severely impact the long-term performance and reliability of the tandem devices.

Protective Barrier Against Environmental Degradation

• Perovskite materials are highly sensitive to moisture and oxygen, which cause rapid degradation. Encapsulation forms a protective barrier that restricts the ingress of these harmful species, thereby significantly prolonging device lifetime.
• Ideal encapsulants are often hydrophobic, transparent insulators with low oxygen transmission rate (OTR) and water vapor transmission rate (WVTR), preventing environmental gases from reaching the perovskite layer.

Thermal and Mechanical Stability

• Perovskite films and devices also degrade under elevated temperatures and mechanical strain, common in outdoor conditions. Encapsulation materials with appropriate mechanical properties can absorb strain and reduce thermomechanical stresses induced by differences in thermal expansion coefficients between layers.
• For example, thermoplastic elastomeric encapsulants like thermoplastic polyurethane (TPU) and thermoplastic polyolefin (TPO) have been investigated for perovskite/silicon tandem modules. These materials enable better mechanical flexibility and thermal cycling stability compared to traditional encapsulants such as ethylene vinyl acetate (EVA), which can be incompatible due to high lamination temperatures.

Optical and Electrical Performance Preservation

• Besides physical protection, encapsulation affects optical properties and thus device performance. Some encapsulants may absorb UV light, reducing the current generated by the perovskite sub-cell, while others improve light in-coupling and reduce reflection losses, enhancing overall performance.
• Optimizing encapsulant selection minimizes efficiency drops after packaging, which is critical for tandem cells where current matching between sub-cells influences power output.

Mitigation of Ion Migration and Lead Leakage

• Encapsulation also helps mitigate ion migration within the perovskite and prevents lead leakage, addressing environmental safety and device stability concerns.
• Advanced encapsulation schemes can improve chemical stability by excluding ambient air and reducing degradation pathways related to ion movement under operational stresses.

Compliance with Stability Testing Standards

• Encapsulated perovskite-silicon tandem solar cells can better withstand rigorous accelerated aging tests such as damp heat exposure and thermal cycling per IEC 61215 standards, which are benchmarks for commercial photovoltaic module durability.
• This capability is essential for translating high lab efficiencies into reliable, commercially viable solar technologies.

In summary, encapsulation techniques for perovskite-silicon tandem solar cells are fundamental to enhancing their stability by:

• Providing a robust barrier against moisture, oxygen, and other environmental factors
• Alleviating thermal and mechanical stresses during operation
• Preserving optical transparency and electrical performance
• Preventing hazardous lead leakage and ion migration
• Enabling compliance with stringent stability certification tests

Together, these roles allow perovskite-silicon tandems to achieve their high-efficiency potential in practical, long-term outdoor applications, advancing the pathway to commercialization of this next-generation photovoltaic technology.