An international team of researchers recently tested a new way of passivating defects in perovskite solar cells. Using a tailored arrangement of atoms, the team managed to overcome challenges related to the formation of a two-dimensional perovskite layer on top of the active cell material, and reach 21.4% conversion efficiency for a 26cm² active area, which is said to be a record for a perovskite device of this size.

Passivation layers, deposited on top of the perovskite material, play an essential role in reducing material defects and unwanted reactions within the material, to improve both performance and stability. One strategy that has been found effective is the use of alkylammonium halides. In many cases these form an additional two-dimensional perovskite layer on top of the perovskite, which can improve device stability but also negatively affect performance.

The research group, that included scientists from institutes in China, Italy, Lithuania, Switzerland and Luxembourg, decided to use an isomer – a different arrangement of atoms – of a previously investigated passivation material, which was shown to be less ready to form a two-dimensional perovskite, but still offered many of the advantages.

Cells fabricated with the passivation reached a conversion efficiency of 23.9% on a device measuring 0.09 cm², and 21.4% when this was scaled up to 26 cm². The devices maintained 85% of this initial efficiency after 1000 hours in operation, and 75% after 1000 hours heated to 85 degrees Celsius in a nitrogen atmosphere.

The team says that its new study demonstrates a new material that could be of interest in perovskite cell manufacturing, and also a new approach in chemical engineering of the passivation layer that could yield even more impressive results. “This study demonstrates that altering functional groups and chemical structures should be an effective strategy to develop novel organic cation passivators with continuous and stable passivation effect,” the team states, “which may pave the way for scaling up perovskite photovoltaics to sizes of commercial relevance.”