Researchers are calling for stronger international standards to detect ultraviolet-induced degradation (UVID) in photovoltaic modules, after identifying “severe” cases of such degradation in operational n-type modules.
Recently, scientists at the U.S. National Renewable Energy Laboratory (NREL) studied passivated emitter and rear totally-diffused (n-PERT) modules in a 3MW commercial PV system that the owner believed were underperforming.
NREL’s research found a high rate of ultraviolet-induced degradation in n-PERT cells.
They observed an annual decline of approximately 2.4% in the system’s field current-voltage (IV) curves compared to the nameplate capacity.
The scientists examined four field-aged modules and two unused spare modules, conducting a series of electrical and physical tests to determine the root cause of the degradation. These tests included module and cell IV scans, electroluminescence and photoluminescence imaging, external quantum efficiency measurements, dark lock-in thermography, and scanning electron microscopy.
Characterization revealed that the modules suffered from power loss due to two degradation modes: surface recombination loss in cells caused by UVID, and high series resistance loss in cells susceptible to metallization paste composition, potentially induced by encapsulant degradation.
After subsequent damp-heat stress testing, further severe degradation in surface resistance was observed in UV-exposed cells.
The researchers noted that the findings do not suggest n-PERT cells are inherently more vulnerable to UVID than other cell types. Instead, specific design decisions—such as passivation layer properties or screen-printed silver paste composition—are key factors.
They emphasized that although the study focused on n-PERT cells, the market’s shift toward other n-type technologies, such as TOPCon and heterojunction, which are also susceptible to UVID, raises concerns about the long-term reliability of photovoltaics.
The researchers stated that the study’s results highlight the need for new standards related to ultraviolet degradation. Current IEC standards are designed to screen for early-stage module failures requiring minimal UV exposure.
“This indicates that as cell and module designs continue to evolve, more stringent UVID qualification standards are needed, along with a more fundamental understanding of UVID degradation modes and their combined stress factors,” they said.
“Our work provides data linking observed field degradation to UVID + damp-heat accelerated test results, helping to establish new UVID stress test qualification standards.”
