A group of researchers from China's Nanchang University and solar module manufacturer Trina Solar have conducted a series of experiments to assess the impact of ultraviolet-induced degradation (UVID) on the performance of tunnel oxide passivating contact (TOPCon) solar modules and have found that this panel type can offer “metastable resilience” in real-world operation.
“Our lab-to-field studies confirm that UVID in TOPCon is a light-recoverable metastable effect with no impact on real-world energy production,” the research's lead author, Zhiwei Li, told pv magazine. “This is critical for improving investor confidence and bankability, and establishes a clear reliability understanding for the industry.”
The researchers conducted UV accelerated aging tests on TOPCon solar cells using a HY-UV-4225 chamber equipped with a metal halide lamp emitting in the 280–400 nm range. During these experiments, the UV intensity was set to 180 W/m², and the module temperature was maintained at 60-65 C, with the samples being placed under short-circuit conditions in a chamber at 50-60 C and exposed to a cumulative irradiation dose of 2 kWh/m² from an 800 W/m² light source spanning 300–1200 nm.
The cells were sandwiched between standard module glass with sealed edges and subjected to a total UV fluence of 30 kWh/m². Following irradiation, the samples were stored in the dark for seven days before being exposed to natural sunlight for one day. Throughout all stages, the front side of the cells was carefully monitored using I–V measurements and photoluminescence imaging to assess performance and capture any changes induced by UV exposure and subsequent light soaking.
Three types of TOPCon cells (C1–C3) with different aluminum oxide (Al₂O₃) and silicon nitride (SiNx) layers were studied, and corresponding modules (M1, M3) were fabricated from these cells. The outdoor testing was conducted in Changzhou, China, with modules mounted at 23° tilt and due south orientation, exposed to unobstructed sunlight and monitored with meteorological sensors. Laboratory solar simulators were used to quantify degradation and recovery under standard test conditions, while energy yield (EY) and performance ratio (PR) were calculated to assess module performance.
The analysis showed that, although M1 modules are more sensitive to UV light, their average EY over five months differs by only 0.17% from that of M3 modules. All TOPCon modules, meanwhile, were found to exhibit a metastable “degradation–recovery” cycle when subjected to UV irradiation, dark storage, and light soaking, driven by synergistic charge redistribution and hydrogen-mediated passivation.
This behavior aligns with previous research, which noted that power losses during dark storage following lab-induced UV degradation. The new field results confirmed that TOPCon modules maintain stable power output under real-world conditions, with light-induced dynamic defect remediation effectively mitigating UV-induced degradation.
“Our findings reveal that TOPCon solar cells exhibit metastable characteristics,” the researchers stressed. “UV irradiation causes power degradation, dark storage exacerbates delayed degradation, and subsequent light soaking treatment almost fully restores cell performance.”
They also explained that the current IEC 61215 standard leaves room for improving UV testing to better reflect the actual impact on field power generation. Both the research community and the PV industry should investigate the threshold UV doses that drive degradation and recovery across different technologies, they concluded.
The experiment was described in “UVID of TOPCon solar cells and the module power output performance in field test,” published in Solar Energy.
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