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

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Researchers from TNO and Fraunhofer ISE conducted a year-long outdoor test on triple-junction perovskite/silicon solar cells, revealing notable performance degradation mainly due to interface delamination and transport-layer failure. The study provides crucial insights into stability challenges for commercial application.

Researchers from TNO and Fraunhofer ISE have documented a significant decline in the efficiency of triple-junction perovskite/silicon solar cells after one year of outdoor testing, with performance dropping from around 17–18% to 13–14%. This development highlights critical stability issues that could affect the commercial viability of perovskite tandem technology.

The study involved outdoor testing of monolithic triple-junction devices in Petten, the Netherlands, installed on rooftops facing south at a 30° tilt. Over the first month, performance stabilized, but long-term data showed a two-phase degradation pattern. Initially, efficiency declined from 17–18% to about 15% by March, then further to 13–14% by April, with continued degradation thereafter.

The primary failure mechanisms identified were voltage loss and encapsulation delamination, rather than intrinsic absorber degradation. Microscopy revealed delamination within the encapsulation layers, indicating mechanical or interlayer adhesion failures rather than moisture ingress. Interface-related losses and shunt pathways were confirmed through EQE and J–V analysis, with spatial inhomogeneities observed via photoluminescence imaging, suggesting partial shunting and non-uniform degradation.

Indoor reliability tests showed good stability under damp-heat conditions but significant losses under thermal cycling and UV exposure, with ultraviolet radiation causing up to 65% efficiency reduction. Despite these issues, the devices maintained an estimated average annual efficiency of around 10%, with performance strongly influenced by irradiance and spectral conditions.

Implications for Commercial Deployment of Perovskite Tandems

This study underscores the stability challenges faced by perovskite tandem solar cells, particularly related to interface integrity and encapsulation durability. The findings indicate that, despite high initial efficiencies, long-term outdoor operation can lead to substantial performance losses, which must be addressed before commercial deployment. Improving interface stability and encapsulation techniques could be critical steps toward making perovskite tandems viable for widespread use, especially in outdoor environments.

Prior Stability Challenges in Perovskite Solar Technologies

Perovskite solar cells have demonstrated high efficiencies in laboratory settings, but their stability under real-world conditions has been a persistent obstacle. Previous indoor tests often showed promising results, yet outdoor exposure has revealed issues such as moisture ingress, UV degradation, and mechanical failure. This latest study provides the first detailed one-year outdoor performance data on triple-junction perovskite devices, which are considered among the most promising for high-efficiency applications.

“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 Aspects of Long-Term Stability and Improvement Strategies

While the study identifies key failure modes, it remains unclear how scalable these findings are to larger modules and different environmental conditions. The effectiveness of potential stability improvements, such as advanced encapsulation or interface engineering, is still under investigation. Further long-term testing and development are needed to confirm whether these degradation pathways can be mitigated for commercial use.

Next Steps in Enhancing Perovskite Device Durability

Researchers plan to develop and test improved encapsulation techniques and interface modifications based on these findings. Larger-area modules and tests under varied environmental conditions are expected to follow, aiming to validate stability improvements. Commercial manufacturers are closely monitoring these developments to assess the readiness of perovskite tandem technology for market deployment.

Key Questions

What are the main degradation mechanisms observed in the study?

The primary degradation mechanisms include voltage loss, encapsulation delamination, and interface degradation, particularly at the transport layers, leading to efficiency decline.

How long do the devices maintain their performance outdoors?

Devices retained about 80% of their initial efficiency after five months, with significant drops occurring by seven months, reaching around 50% efficiency.

Are these findings applicable to larger solar modules?

The study was conducted on small (1 cm x 1 cm) test cells; scaling up to larger modules may introduce additional challenges, and further testing is needed to confirm applicability.

What improvements are being considered to enhance stability?

Potential strategies include better encapsulation materials, interface engineering to reduce delamination, and improved charge transport layers resistant to thermal and UV stress.

When might we see commercially available stable perovskite tandem solar panels?

While progress is ongoing, widespread commercial deployment depends on overcoming stability hurdles; optimistic timelines suggest several years of further research and development.

Source: PV Magazine