Image: UNSW
UNSW researchers have developed a new method that reveals how solar cells are damaged by ultraviolet radiation – and how they can naturally repair themselves using sunlight.
The research, led by UNSW Sydney scientia professor Xiaojing Hao and published in Energy & Environmental Science, allows scientists to observe chemical changes inside high-efficiency silicon solar cells as they degrade under UV exposure and then recover under normal operating conditions.
Engineers used a non-destructive monitoring technique that tracks material-level changes inside a working solar cell, providing unprecedented insight into a long-observed but poorly understood phenomenon known as ultraviolet-induced degradation (UVID). Silicon solar cells are known to lose efficiency over time when exposed to UV radiation, with some studies reporting performance drops of up to 10 per cent after the equivalent of 2000 hours of accelerated UV testing.
While photovoltaic experts have long known that some of this lost performance can be recovered when cells are exposed to sunlight during normal operation, the underlying mechanism had remained unclear. As a result, it has been difficult to determine whether UV-related performance losses are permanent or how accurately 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 applying ultraviolet Raman spectroscopy to operating solar cells. The technique involves shining a laser on a material and analysing how the scattered light reveals molecular vibrations, allowing researchers to identify chemical bonding changes without damaging the cell.
“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.
At the microscopic level, the researchers observed that UV light reconfigures chemical bonds involving hydrogen, silicon and boron atoms near the cell surface, weakening surface quality and reducing performance. When the cells were later exposed to visible light, those chemical structures returned to their original state as hydrogen atoms migrated back, repairing broken bonds.
“This confirms that recovery is not just an electrical effect,” Dr Liu said. “The material itself is repairing at the atomic level.”
The findings have significant implications for how solar panels are tested, designed and certified. Current accelerated ageing tests expose cells to intense UV radiation over short periods, potentially overstating long-term degradation if some effects are reversible under normal sunlight.
By distinguishing between temporary and permanent changes, the new monitoring method provides a scientific foundation for improving testing standards. It also offers practical advantages, allowing UV sensitivity to be detected in seconds rather than days, without destroying the cell.
Professor Hao said the technique could eventually be used on production lines for rapid quality control. “With better monitoring tools, we can design better tests, better panels, and ultimately more reliable solar energy systems,” she said.
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