A team led by scientists from the Department of Chemistry at Imperial recently studied the mechanism that causes perovskite solar cells to degrade quickly, discovering that this breakdown is due to the formation of ‘superoxides’ that attack the perovskite material. Now, the team went on to determine how the superoxides form and how they attack the perovskite material, and proposed possible solutions to the problem.

Working with researchers at the University of Bath, the team found that superoxide formation is helped by spaces in the structure of the perovskite normally taken up by molecules of iodide. Although iodide is a component of the perovskite material itself, there are defects where iodide is missing. These vacant spots are then used in the formation of superoxides.

The team found that while dosing the material with extra iodide after manufacturing improved the stability, a more permanent solution could be to engineer the iodide defects out. Lead author of the new study said: “After identifying the role of iodide defects in generating superoxide, we could successfully improve the material stability by filling the vacancies with additional iodide ions. This open up a new way of optimizing the material for enhanced stability by controlling the type and density of defects present.”

The team added: “We have now provided a pathway to understand this process at the atomic scale and allow the design of devices with improved stability”. Currently, the only way of protecting perovskite cells from degradation by air and light is encapsulation in glass. However, perovskite solar cells are made from flexible materials designed to be used in a range of settings, so the glass encasement severely limits their function and adds weight and cost. Improving the materials to render encapsulation unnecessary is obviously considered a much better solution.

The team hopes to next test the stability of the cells in real-world settings. The cells would be exposed to a combination of both oxygen and moisture, testing the cells in more relevant scenarios.

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