Next-gen solar cells pass strict international tests

Wednesday, 03 June, 2020

Next-gen solar cells pass strict international tests

Scientists from UNSW and the University of Sydney have produced a new generation of experimental solar energy cells that pass strict International Electrotechnical Commission testing standards for heat and humidity, meaning they are ready to take the next steps towards commercialisation.

Solar energy systems are now widespread in both industry and domestic housing. Most current systems rely on silicon to convert sunlight into useful energy; however, the energy conversion rate of silicon in solar panels is close to reaching its natural limits.

Scientists have thus been exploring new materials that can be stacked on top of silicon in order to improve energy conversion rates. One of the most promising materials to date is the metal halide perovskite, which may even outperform silicon on its own.

“They are very inexpensive, 500 times thinner than silicon and are therefore flexible and ultralightweight,” said Professor Anita Ho-Baillie from the University of Sydney, who led the new research. “They also have tremendous energy enabling properties and high solar conversion rates.”

In experimental form, the past 10 years has seen the performance of perovskites cells improve from low levels to being able to convert 25.2% of energy from the Sun into electricity; in comparison, it took about 40 years for scientists to develop silicon-cell conversion rates of 26.7%. However, unprotected perovskite cells do not have the durability of silicon-based cells, so they are not yet commercially viable.

“Perovskite cells will need to stack up against the current commercial standards,” Prof Ho-Baillie said. “That’s what is so exciting about our research. We have shown that we can drastically improve their thermal stability.”

Under continual exposure to the Sun and other elements, solar panels experience extremes of heat and humidity. Experiments have shown that under such stress, unprotected perovskite cells become unstable, releasing gas from within their structures.

“Understanding this process, called ‘outgassing’, is a central part of our work to develop this technology and to improve its durability,” Prof Ho-Baillie said.

For the first time, the research team used gas chromatography–mass spectrometry (GC-MS) to identify the signature volatile products and decomposition pathways of the thermally stressed hybrid perovskites commonly used in high-performance cells. Using this method, they found that a low-cost polymer-glass stack with a pressure-tight seal was effective in suppressing the perovskite outgassing — the process that leads to its decomposition.

When put to strict international testing standards, the team’s cells outperformed expectations. Prof Ho-Baillie said, “Another exciting outcome of our research is that we are able to stabilise perovskite cells under the harsh International Electrotechnical Commission standard environmental testing conditions. Not only did the cells pass the thermal cycling tests, they exceeded the demanding requirements of damp-heat and humidity-freeze tests as well.”

These tests help determine if solar cell modules can withstand the effects of outdoor operating conditions by exposing them to repeated temperature cycling between -40 and 85°C, as well as exposure to 85% relative humidity. Specifically, the perovskite solar cells survived more than 1800 hours of the IEC Damp Heat test and 75 cycles of Humidity Freeze test, exceeding the requirements of the IEC61215:2016 standard.

Published in the journal Science, the research findings mark an important step towards the commercial viability of perovskite solar cells. Prof Ho-Baillie concluded, “We expect this work will contribute to advances for stabilising perovskite solar cells, increasing their commercialisation prospects.”

Image caption: A sample of some of the perovskite cells used in the experiment. Image credit: UNSW.

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