From pv magazine Global
NREL researchers have fabricated an all-perovskite tandem solar cell with perovskite films to show reduced defect density and achieve a power conversion efficiency of 27.1%.
The new cell builds on another inverted perovskite solar cell fabricated with p-i-n structure, which was unveiled by the research group in September. This device, according to the scientists, was able to retain 87% of its original efficiency after 2,400 hours of operation at 55 C.
For the new cell, the group did not use an antisolvent to create a uniform perovskite film and used instead gas quenching, which consists of cooling the parts of a material down from critical temperature quickly in order to strengthen and harden. It is commonly used to maintain the properties associated with a crystalline structure or phase distribution.
“The result addressed the problem of the bromine and iodine separating, resulting in a perovskite film with improved structural and optoelectronic properties,” the scientists explained. “The gas-quenching process, when applied to high-bromine-content perovskite chemicals, forces the crystals to grow together, tightly packed from top to bottom, so they become like a single grain and significantly reduces the number of defects.”
Through this approach, the researchers were able to achieve a 20% efficiency for the wide-bandgap layer, which also showed operational stability, with less than 5% degradation over 1,100 hours.
When connected to a 1.25 eV narrow-bandgap bottom perovskite cell, the perovskite layer was able to bring the overall cell efficiency to 27.1% and its open-circuit voltage to 2.2 V.
“The gas-quench method is a general way for improving the performance of wide-bandgap perovskite solar cells,” said the scientists.
They presented the cell tech in “Compositional texture engineering for highly stable wide-bandgap perovskite solar cells,” which was recently published in Science.
“The new growth approach demonstrated the potential of high-performance all-perovskite tandem devices and advanced the development of other perovskite-based tandem architectures such as those that incorporate silicon,” they concluded.
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