Solar cells can self-heal after sunburn, and knowing this could slash the cost of making them

The cosmetics industry will tell you that sun damage is the worst thing to happen to your skin, and until now the photovoltaic industry held similar views about solar cells.

But unlike in humans, much of the damage done by ultraviolet rays to solar panels is very reversible, according to new research out of the University of New South Wales (UNSW). In fact, it appears that solar cells can heal themselves.

The findings from the UNSW research could cut the cost of making solar modules and improve their efficiency because now researchers — and manufacturers — can see in real time what UV radiation is doing inside a solar cell while it is operating.

Furthermore, they can test and see within seconds whether a cell is vulnerable to UV damage. 

“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 Ziheng Liu, corresponding author of the paper in Energy & Environmental Science, in a statement.

“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.”

The UNSW method of using ultraviolet Raman spectroscopy, which uses lasers to scatter light and reveal a material’s molecular vibrations, allowed Liu and his co-authors to see what is happening in real time without having to physically shred the panel, or rely on electrical output readings.

“This approach helps distinguish between true long-term degradation and reversible changes,” Liu said.

“That distinction is essential for accurate lifetime prediction.”

Cells that heal themselves

The kind of accelerated testing to simulate real world UV exposure has led to suggestions of degradation as high as 10 per cent, the paper says.

Even though the photovoltaic industry has for some time known that panels can recover some of that performance, they haven’t known why.  

Currently, solar cells are tested for UV damage resistance during the manufacturing process. 

That method involves intense blasts of UV radiation at a cell to simulate 2000 hours of exposure, which is then shredded to see what happened. It’s a process that can take between days and weeks, the UNSW paper says. 

But in the real world “normal” sunlight actually heals the damage done by UV rays, the UNSW team found when looking at TOPCon cells.

Solar cells rely on hydrogen bonding with the silicon to increase efficiency.

But UV radiation breaks these bonds. Modern cells have a buffer layer of magnesium or aluminium oxides.

But if they don’t actually need this layer, or don’t need it to be as thick, that will cut the cost of making modules and improve electrical efficiency at the same time, Liu told Renew Economy.

He says 10-20 minutes of “normal” sunlight allows those bonds to reform.

It means manufacturers are likely to be over-estimating the amount of irreversible damage happening over the life of a solar cell and over-engineering their panels.

Different types of cells have different levels of reversibility, the paper says, but it focused on TOPCon as it’s predicted to be the dominant technology in the coming years. 

Not only can these panels repair UV damage themselves, but manufacturers could get by with a thicker aluminium oxide film and a thinner silicon-nitrogen layer.

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