Long lifetime for perovskite solar cell
Researchers in Germany have developed a perovskite solar cell that could have a lifetime as high as 20,000 hours, or nearly 30 months, with a high conversion efficiency.
Perovskite materials are low cost and easy to manufacture and challenging silicon for efficiency, But they struggle with lifetime, decomposing relatively quickly in a few days or weeks, which is a challenge for solar panel makers.
The team at the Helmholtz Institute Erlangen-Nuremberg of the Forschungszentrum Jülich explored the range of perovskite materials specifically to find ones that could have a longer lifetime.
The researchers systematically tested hundreds of different perovskite mixtures for their suitability using high-throughput methods. The researchers then used the best ones to build their cell. “Even if you only rely on proven components, you come up with tremendous numbers of possible compositions that we can produce and test automatically using our methods. In other studies, there are sometimes even significantly more,” said Dr. Yicheng Zhao. “That is why we need to use a systematic approach to identify the best material combinations.“
In tests at elevated temperature and illumination over 1450 hours of operation, they developed a perovskite-based cell that retained 99 percent of its initial efficiency. The results were published in Nature Energy.
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A characteristic feature of perovskites is a specific crystal structure. Numerous material combinations of different atoms and molecules are possible, some of which exhibit ferroelectric, superconducting or photovoltaic properties. Layers of perovskite cells, which are only a few hundred nanometers thick, can also be applied to conventional silicon solar cells to create tandem cells.
“The Achilles’ heel of perovskite solar cells is their low durability,” said Prof. Christoph Brabec of the Helmholtz Institute Erlangen-Nuremberg (HI ERN). “Classic silicon modules are quite durable. Even after more than 20 years in practical use, they lose little of their performance.”
Next: Perovskite stability
“The solar cell we have now presented in Nature Energy, on the other hand, impresses with its exceptional stability. The values are certainly among the best ever measured for a planar perovskite solar cell in a long-term test,” said Brabec. The illuminated cell had to survive 1450 hours at elevated temperatures around 65 degrees Celsius in the laboratory and remained largely stable throughout the test period. At the end, it still had 99 percent of its initial efficiency.
“Long-term prediction is always difficult. But the perovskite solar cell we have now developed could certainly be operated for more than 20,000 hours under normal circumstances,” said Brabec.
Another important optimization step concerns the stable contacts of the perovskite within the cell, which is built up in several thin layers. The ionic dopants or metal oxide nanoparticles commonly used to contact the cell tend to undergo secondary reactions at higher temperatures. This reactions can even lead to corrosion of the metal electrodes, as the researchers at HI ERN were able to demonstrate through measurements and scanning electron microscopy.
“To improve stability at the contact point, we packed the entire electrode in a kind of protective shell,” said Zhao said. A new double-layer polymer structure, with the bottom side undoped and the top side doped with a non-ionic dopant, protects against degradation and ensures that the contact is maintained. On the one hand, this architecture protects the very sensitive interface to the perovskite, and on the other hand, it shows exceptionally stable conductivity, even at elevated temperatures.
For the future, the HI ERN researchers are now aiming for further efficiency improvements. “With an efficiency of 20.9 percent, the tested cell does not yet fully exploit the potential. 24 to 25 percent should be possible in the near future,” said Zhao.
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