UNSW researchers have devised a process that identifies exactly how solar cells are damaged by ultraviolet radiation – and what happens when they naturally recover thanks to the sun.
Engineers have developed a way to monitor solar cells at a microscopic level while they are operating – to discover exactly how damage caused by ultraviolet light can be naturally repaired.
The new monitoring method allows experts to directly observe chemical changes inside high-efficiency silicon solar cells as they degrade under UV exposure, which in turn is expected to help develop processes that can help the cells recover using normal sunlight.
The research, led by UNSW Sydney Scientia Professor Xiaojing Hao, and published in Energy & Environmental Science, could significantly transform how solar panels are tested, designed, and certified for long-term outdoor use.
"This new method can be used directly on the production line to quickly check how well solar cells resist UV damage, making it useful for future quality control during manufacturing," says Prof. Hao.
Silicon solar cells suffer a reduction in their efficiency and performance over time due to exposure to ultraviolet radiation – known as ultraviolet-induced degradation (UVID).
Some previous studies have shown the drop in performance can be as high as 10% after the equivalent of 2000 hours exposure to UV radiation during accelerated testing.
Photovoltaic experts have long known that solar cells can recover some of this lost performance when exposed to sunlight during normal operation – but this recovery had only been observed in terms of electrical output and it remained a mystery what was actually happening inside the material.
Without that understanding, it has been difficult to determine whether UV-related performance losses are permanent, how serious they are, and how well current testing standards reflect real-world conditions.
The UNSW-led team, including Dr Ziheng Liu, Dr Pengfei Zhang and Dr Caixia Li, addressed this challenge by developing a new, non-destructive monitoring technique that can track material-level changes inside a working solar cell.
They used a technique called ultraviolet Raman spectroscopy that identifies a material by shining a laser on it and analysing how the light scatters to reveal the material's molecular vibrations.
This method allowed the researchers to observe chemical bonding near the surface of the solar cell while it was being exposed to UV light and during recovery under visible light. At all times the cell remained intact. And it can be used for cells operating under realistic conditions.
"This technique works a bit like a camera. Instead of just measuring how much power the cell produces, we can directly see how the material itself is changing in real time," said Dr Liu, corresponding author of the paper.
"Normally we can only measure the power output. That has been observed already by many people, but with this new method we are also explaining the mechanism and we can see the change at a material level," added Dr Liu.
Previously, studying such processes required cutting cells apart or relying on indirect electrical measurements, making it impossible to observe reversible changes as they occurred.
With the new monitoring method, the researchers were able to observe how the chemical changes were happening and understand better how the damage was being repaired using normal light.
At the microscopic level, UV light reconfigures certain chemical bonds involving hydrogen, silicon, and boron atoms near the cell surface. This weakens surface layer quality and reduces performance. Crucially, the team was able to observe these bond changes directly for the first time.
When the cell was later exposed to normal visible light, the researchers saw the chemical structure return to its original state. Hydrogen atoms migrated back toward the surface, broken bonds were repaired, and the material recovered.
"This confirms that recovery is not just an electrical effect," said Dr Liu, from UNSW's School of Photovoltaic and Renewable Energy Engineering. "The material itself is repairing at the atomic level."
Why the monitoring method matters
The ability to directly observe reversible material changes has major implications for the solar industry.
Solar panels are certified using accelerated ageing tests that expose cells to intense UV radiation over short periods to simulate years of outdoor use. However, if a degradation process is reversible under normal sunlight, such tests may overestimate the loss and induce permanent damage that will not happen in the real outdoor working conditions.
By revealing exactly which changes are temporary and which are lasting, the new monitoring method provides a scientific foundation for improving these tests.
"This approach helps distinguish between true long-term degradation and reversible changes," Dr Liu said. "That distinction is essential for accurate lifetime prediction."
Beyond its scientific insights, the monitoring technique offers practical advantages.
Traditional UV degradation tests can take days or weeks and often require destructive analysis. In contrast, the Raman-based method can detect UV sensitivity in seconds while leaving the solar cell intact.
This speed and realism make it well suited for use during manufacturing, where rapid feedback is critical. The researchers say the method could be used to screen new materials, processing conditions, or design changes before cells are built into full solar panels.
In the future, it could even be adapted for in-line quality control, allowing manufacturers to identify potential UV-related issues early in production.
Supporting better solar panel design
The monitoring, method also helps explain why some solar cells degrade more than others.
By directly observing material-level changes, the researchers showed how design choices such as passivation layer thickness or surface coating properties can affect how hydrogen moves during UV exposure and recovery. This knowledge would allow manufacturers to make informed trade-offs between peak efficiency, durability, and cost.
Importantly, the study - supported by the ARC Research Hub for Photovoltaic Solar Panel Recycling and Sustainability (PVRS) - shows that a solar cell that temporarily degrades but then recovers may actually outperform a more costly design that is fundamentally more UV-resistant over its lifetime.
"This work gives us a clearer picture of how solar cells behave in the real world," Prof. Hao says. "With better monitoring tools, we can design better tests, better panels, and ultimately more reliable solar energy systems."
