Solmar Insights
A new study by US researchers has identified substantial variation in UV-induced degradation of TOPCon solar cells from different commercial manufacturers, with recorded short-circuit current losses reaching as high as 4% for certain suppliers. The findings highlight the operational risks and quality differentials facing utility-scale solar asset buyers and developers working with n-type TOPCon technologies.
Key figures
Up to 4% short-circuit current density loss (Vendors 2 and 3)
Less than 1% loss in Vendor 1 TOPCon cells
UV-range EQE loss: ~40% for Vendor 2, 10% for Vendors 1 and 3
Significant variability between manufacturers
US-based researchers carried out a technical analysis on unencapsulated M10 bifacial TOPCon solar cells from three undisclosed commercial vendors. These cells, all intended for module production, were designated as Vendor 1, Vendor 2, and Vendor 3. The work focused on metastable dark degradation and light-assisted recovery after ultraviolet exposure, issues with heightened relevance as utility-scale projects move toward TOPCon architectures.
The analysis revealed striking differences in degradation and recovery responses to UV stress between cells from different vendors. While all three types of cells shared nominally identical architectures, the extent of UV-induced performance loss diverged widely based on proprietary materials and manufacturing approaches.
For instance, the quantum efficiency loss resulting from UV light reached around 40% in Vendor 2’s products, compared with approximately 10% for both Vendor 1 and Vendor 3. Likewise, only Vendor 1’s cells limited short-circuit current density loss to under 1%, while the other two vendors saw about 4% drops, a critical distinction for project yield modeling and equipment selection.
Mechanisms and performance impacts
The research detailed how small differences in materials, such as layer thickness, composition, and microstructure, can go undetected during initial performance testing, but become pronounced over time due to metastable dark degradation and UV-related effects. Even within the same nominal design, vendor-specific process controls and material choices dictated how each cell performed after extended light and dark cycling.
After exposure to UV, the affected solar cells were subjected to localized external quantum efficiency measurements. The process included periods of controlled light soaking and subsequent dark storage to gauge both degradation and the potential for light-assisted recovery. The study found that, despite acceleration of UV-induced losses, there was an opportunity for partial recovery if cells were exposed to light at wavelengths between 320 nm and 340 nm.
Such degradations and recoveries in real-world deployments have direct implications for annual energy yield, long-term bankability assessments, and module warranty negotiations, especially as daily sunlight and night cycles trigger repeating rounds of stress and healing in deployed arrays.
Testing and modeling implications
The results indicate a need for revised module testing standards, particularly concerning prequalification and performance guarantees in power purchase agreements (PPAs) and project finance. Researchers recommend that manufacturers and independent engineers employ controlled light soaking protocols before performance testing, as significant capacity could be temporarily dependent on recovery cycles often missed in single-shot flash tests.
The daily cycles of degradation in darkness and partial recovery in light observed across the product samples suggest that traditional yield models, which often ignore these metastable effects, may either overstate or understate the true output variability of TOPCon-based projects. Asset owners should press vendors on their light and dark cycle test data, ensuring that recovery and degradation rates are reflected in performance forecasts and contractual guarantees.
In corporate procurement and merchant offtake negotiations, assumptions based on assumed uniformity of TOPCon performance across suppliers are now clearly questionable. Buyers evaluating options for large-scale installations will need to adjust bankability scoring and component selection methodologies, factoring in both initial flash test data and independent cycling analysis.
Vendor selection and project risk
This study’s demonstration of performance divergence between commercially available TOPCon modules raises the stakes for supply chain due diligence. Project developers and investors with exposure to high-irradiance markets or projects with stringent performance guarantees should revisit vendor qualification processes, focusing not just on factory throughput and certifications but also on real-world UV durability data.
For engineering, procurement, and construction (EPC) contractors and asset owners, choosing vendors with independently validated low UV-induced degradation could offer a direct boost to performance ratio and mitigate risks that emerge only after prolonged field use. This is particularly relevant for portfolios in the US Southwest and other solar-rich regions where intense UV exposure accelerates degradation phenomena.
Ultimately, these findings may also catalyze further segmentation in supply agreements, as buyers seek assurances beyond datasheet specifications, explicitly demanding third-party-verified post-UV stress data or adopting “burn-in” requirements prior to module shipment and installation.
Forecast for commercial solar deployment
This new understanding of vendor-to-vendor risk in TOPCon module degradation will shape asset management and procurement strategies for the next wave of US solar expansion. As n-type TOPCon technology sees increased market share for utility-scale projects between 2026 and 2028, buyers and investors will closely monitor manufacturer performance claims and third-party test results related to UV stability.
PPA price negotiations and portfolio risk calculations will increasingly incorporate these degradation and recovery findings. For those seeking project finance or entering offtake agreements in competitive ISO/RTO markets, clear evidence of cell resilience under UV exposure could play a decisive role. Developers may push for extended performance guarantees or require suppliers to conduct on-site post-installation testing as part of commissioning protocols, closing the gap between lab data and fielded asset output.
What this means for buyers
Equipment sourcing for utility-scale solar projects in the US now faces a clear differentiation in TOPCon module durability under UV exposure. A recorded 4% short-circuit current density loss in Vendor 2 and 3 cells means PPA, yield, and warranty models must reflect non-uniform degradation. Buyers commissioning projects this quarter should require UV durability test data and consider adjusting vendor scoring to prioritize UV resilience.
Reporting via the original publisher
