One-year outdoor testing reveals degradation paths in perovskite tandem solar cells

TL;DR

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Researchers from TNO and Fraunhofer ISE conducted a one-year outdoor performance test on triple-junction perovskite/silicon solar cells. The study found a notable efficiency drop from about 17-18% to 13-14%, mainly due to interface degradation and encapsulation delamination. These findings provide critical insights into the stability challenges facing perovskite tandem technology.

Researchers from TNO and Fraunhofer ISE have conducted a one-year outdoor performance test on triple-junction perovskite/perovskite/silicon solar cells, revealing a significant efficiency decline driven by multi-stage degradation mechanisms. The study’s findings highlight persistent stability challenges in these high-performance devices, which are crucial for advancing commercial viability.

The outdoor test was performed in Petten, Netherlands, using rooftop-mounted modules with a south-facing tilt of 30°. Initial efficiency was around 17–18%, but over the course of a year, it declined to approximately 13–14%. The primary degradation mechanisms identified were voltage loss, encapsulation delamination, and interface deterioration, rather than intrinsic instability of the perovskite layers.

Microscopy analysis showed that delamination occurred within the encapsulation stack, not at the active junctions, indicating mechanical or adhesion failures. Performance analysis via EQE and J–V measurements suggested that interface-related losses and shunt pathways, rather than bandgap shifts or absorber degradation, were responsible for the efficiency decline. Post-exposure photoluminescence imaging revealed spatial inhomogeneity, with the middle perovskite layer maintaining current flow while the top junction weakened, pointing to partial shunting and non-uniform degradation as key issues.

Indoor tests confirmed good stability under damp-heat conditions but showed significant losses under thermal cycling and UV exposure, with UV alone causing up to 65% degradation. Despite these issues, the devices maintained an estimated average annual efficiency of around 10%, with performance heavily influenced by irradiance and spectral conditions. The researchers noted that the top junction was the least stable component, and edge-localized shunting developed in the middle junction, likely driven by sustained elevated temperatures.

Impact of Degradation on Commercial Viability of Perovskite Tandems

The findings highlight critical stability challenges that must be addressed before perovskite tandem solar cells can be widely adopted commercially. The observed degradation pathways—particularly interface failures and encapsulation delamination—limit long-term performance and reliability, which are essential for large-scale deployment. Understanding these failure modes informs future device design, emphasizing the need for improved encapsulation and interface engineering to enhance durability and reduce performance loss over time.

Previous Stability Assessments of Perovskite Solar Technologies

While perovskite solar cells have demonstrated high efficiencies in laboratory settings, translating this performance into outdoor conditions has proven challenging. Prior studies have shown issues with moisture ingress, thermal instability, and UV degradation, but long-term outdoor data has been limited. This recent study is among the first to monitor the outdoor performance of triple-junction perovskite devices over a full year, providing valuable insights into real-world degradation mechanisms and their impact on efficiency retention.

“The samples achieved 80% of the initial power conversion efficiency after five months of outdoor operation, and 50% after seven months.”

— an anonymous researcher

Unresolved Questions About Long-Term Stability and Mitigation

It remains unclear how these degradation pathways can be mitigated through device engineering or materials improvements. The long-term stability beyond one year, especially under different environmental conditions, is still unconfirmed. Further research is needed to determine whether encapsulation strategies and interface modifications can significantly extend device lifespan.

Next Steps in Improving Perovskite Tandem Durability

Researchers will focus on developing more robust encapsulation techniques and interface engineering to mitigate delamination and interface degradation. Extended outdoor testing under varied climatic conditions is planned to assess long-term stability. Additionally, efforts are underway to optimize device architecture to enhance durability without compromising efficiency, aiming for commercially viable, stable perovskite tandem solar modules.

Key Questions

What are the main causes of efficiency loss in these perovskite tandem cells?

The primary causes include interface-related losses, encapsulation delamination, and degradation of charge transport layers, rather than intrinsic instability of the perovskite absorber itself.

How long did the tested devices maintain their initial efficiency?

They maintained about 80% of their initial efficiency after five months and roughly 50% after seven months of outdoor exposure.

Are these degradation issues unique to this device configuration?

The issues observed relate to specific device architecture and materials used, particularly the interface and encapsulation layers. These challenges are common in perovskite devices but vary with design and material choices.

What improvements are being considered to enhance stability?

Researchers are exploring advanced encapsulation methods, interface modification, and more stable charge transport layers to reduce delamination and interface degradation.

Will this degradation limit commercial deployment of perovskite tandem solar cells?

While the findings highlight significant stability challenges, ongoing research aims to address these issues. Improved device designs could make commercial deployment feasible in the future.

Source: PV Magazine