Researchers at the University of Washington, the Massachusetts Institute of Technology and the University of Oxford have been trying to find ways to repair inherent perovskite defects in order to improve the efficiency of solar cells. They showed that the photons they shined on the perovskite cells had a therapeutic effect, and exposure to intense visible light increased the energy conversion efficiency of the perovskite crystals.
Using perovskite crystals synthesized at Oxford University, the scientists showed that intense light exposure helped crystals repair themselves by physically transporting iodine during illumination. They used two powerful imaging techniques to show that iodine ions within perovskite crystals moved away from intense light.
The team hypothesize that the unique chemical environment at the surface of synthetic perovskite crystals explains this movement, since many of the defects in these crystals lie along the surface, and that may cause negatively charged electrons to pile up at the crystal surface. If so, then upon shining light on the surface, negatively charged ions within the crystal — like iodide — will want to move away and that may explain how light helps these crystals heal, at least on a temporary basis.
The team's experiments reveal that light has only a temporary healing effect on the solar cell crystals, but they aim to find processing routes or treatments that make their repairs permanent.