In the study, the researchers altered the chemical composition of the perovskite layers by adding potassium iodide to perovskite inks, which then self-assemble into thin films. The technique is compatible with roll-to-roll processes, which means it is scalable and inexpensive. The potassium iodide formed a 'decorative' layer on top of the perovskite which had the effect of 'healing' the traps so that the electrons could move more freely, as well as immobilising the ion movement, which makes the material more stable "

Nice catch Sunny!