23.1% Efficiency For All-Perovskite Tandem Solar Cells

A team of researchers from the US National Renewable Energy Laboratory (NREL) claim to have achieved a 23.1% all-perovskite tandem solar cell efficiency on glass that can be deployed for solar powered vehicles. They managed this feat with the help of NREL’s new perovskite material called Apex Flex.
The team calls it an all-perovskite technology since it covers all aspects aimed to be achieved through a tandem cell which layers 2 perovskite materials to bring forth a combined efficiency ‘higher than any other thin-film technology outside of III-V materials’. The III-V grade materials are fit enough for spaceship quality, and NREL claims compared to this Apex Flex is 200 times lower cost.
Conventional method of pitting 2 perovskites together under a tandem arrangement has 2 main challenges that prevent higher efficiencies. These relate to bottom cell getting damaged during top cell processing and achieving high open-circuit voltage of the wide-gap subcell.
To create this all perovskite solar cell with an efficiency equaling that achieved by tandem cells, NREL engineered a ‘dense and thin’ recombination layer between 2 perovskite materials or wide-bandgap perovskite it calls Apex Flex that eliminates shunt paths. Using less bromine they also altered the layer’s crystal structure using a different molecular alloy with high stability and efficiency, and managed to achieve 2-terminal all-perovskite tandem solar cells with 23.1% power conversion efficiency on glass and 21.3% on flexible plastic substrates.
“Pairing more than one metal halide perovskite absorber in a single solar cell enables a truly differentiated solar technology that is high-efficiency, low-cost, and lightweight,” said fellow co-creator and NREL scientist Axel Palmstrom. “This collaborative effort has brought all-perovskite tandems closer to commercial reality, and we are excited to see their real-world applications in the near future.”
Even though the researchers admit that Apex Flex is still not ready to meet the 25 years to 30 years lifetime of a utility or residential solar system, they are confident it can be useful for vehicular application. At the same time, it can be explored for use in the future for wearable and flexible solar panels.
The research by NREL Researchers David Moore and Axel Palmstrom was published by scientific journal Joule under the title Enabling Flexible All-Perovskite Tandem Solar Cells.
In an earlier research, the NREL and Northern Illinois University (NIU) created a safety belt for perovskite solar cells without impacting cell performance (see Researchers Create Safety Belt For Perovskite Solar Cells).