Wednesday, August 19, 2026
When it comes to analogies to explain how solar cells are manufactured, cake baking is not one that immediately jumps to mind. But according to a group of engineers from the University of New South Wales (UNSW), that’s exactly the skill they’re trying to emulate to improve tandem solar cell efficiency.
Engineering researchers from UNSW, led by Scientia Professor Xiaojing Hao, from UNSW’s School of Photovoltaic and Renewable Energy Engineering, have started applying lessons from baking to better understand how to improve solar cells.
The researchers are working with a material known as CZTS – a promising option for tandem solar cell semiconductors that is made from copper, zinc, tin and sulphur; a group of materials much more abundant and environmentally friendly than some used in semiconductor production.
But despite the promise, CZTS has not yet been able to reach the efficiencies needed for commercial adoption.
According to the UNSW researchers, the problem for CZTS semiconductors has been the creation of tiny defects during the manufacturing of the material.
This is where baking enters the picture.
“The cake analogy is really apt because that’s exactly what we are doing,” said Hao.
“With a cake you mix all the different ingredients and put it into the oven. We do a similar thing with solar cell material, except it goes into a furnace.”
And, as with baking, it is not always as easy as mixing everything together and hoping for the best during the cooking process.
“A lot of people think once you have the right amount of ingredients for the cake, then everything will be fine,” said Hao.
“But sometimes that’s not the case. You need to keep the ingredients uniformly distributed from the very beginning and throughout the cooking process.
“The journey matters just as much as the destination. That’s the major design principle we’ve implemented in this research to discover why CZTS can have the imperfections.”
When the researchers investigated what happened during the first moments of the high-temperature manufacturing process, they found that the copper was liable to move away from where it was needed – a seemingly small change that nevertheless triggered the formation of unwanted impurities and tiny structural defects.
And these small defects have an outsize impact on a solar cell’s ability to convert light into solar energy.
“When one ingredient drifts away, it forms another phase, which is technically another material,” Professor Hao explains. “So when the crystal grows, you end up with impurities and tiny imperfections inside it.
“It also causes disorder inside the crystal. Those point defects can trap the photo-generated carriers, and that causes the low efficiency of solar cells.
“Voltage is a direct measure of the energy loss inside the solar cells. Every detrimental defect reduces the voltage. Defect control determines the final efficiency and how much energy can be converted from sunlight.”
By strengthening the copper-sulphur bonding during the initial thermal reaction, the UNSW team were able to significantly reduced defect formation and enable the material to achieve record voltage performance for this class of CZTS solar cell of 12.4 per cent.
And while this efficiency is well below commercial silicon solar cells, the researchers believe it is significant as it addresses one of the technology’s longest-standing scientific challenges.
Similarly, they also believe their discovery can be applied to different semiconductor materials used in future solar technologies. As co-author Dr Ao Wang explains, it is not enough to simply make sure all the starting ingredients are correct.
“Most people focus on getting the right recipe and think the thermal process is a black box,” said Wang.
“They assume that once the ingredients are mixed well then the cake, or in this case the solar cell, will naturally come out as intended.
“But this is not the case. If the butter starts separating in the first few minutes of baking, even a perfect recipe won’t produce a perfect cake.”
Just as with CZTS, so too with other semiconductor materials which often consist of several different chemical elements, making them susceptible to similar issues during manufacturing.
And according to Scientia Prof. Hao, controlling how ingredients behave during the earliest stage of fabrication could have important implications across the field.
“The defect control strategy we’ve developed is going to be really useful for designing and optimising other compound semiconductors,” she says.
“I hope our defect control technology and principle can really be used by other people who are designing more top-cell candidates for tandem solar cells.
“The design principle isn’t only about this material. It’s about not only looking at the final recipe, we need to design from when we’re mixing the ingredients and keep them uniformly distributed. The ingredients may change from one semiconductor to another, but the design principle is the same.”
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Joshua S. Hill is a Melbourne-based journalist who has been writing about climate change, clean technology, and electric vehicles for over 15 years. He has been reporting on electric vehicles and clean technologies for Renew Economy and The Driven since 2012. His preferred mode of transport is his feet.
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