Matthew T. Klug

An international team of researchers from the University of Cambridge, Massachusetts Institute of Technology, University of Oxford, University of Bath, and Delft University of Technology have discovered that exposing perovskite solar cells—a compound made of lead or tin—to daylight and certain levels of humidity can permanently fix any existing defects. Perovskite cells are used as an alternative to current silicone-based solar cells which are known to have a higher market price. "They are cheap and easy to produce," noted the press release. "And in just a few short years of development, perovskites have become almost as efficient as silicon at converting sunlight into electricity." Despite all the benefits this crystalline-structure compound brings to the world of solar energy, they are easily prone to defects. Known as "traps," these defects can literally trap electrons before energy is released.

In a previous study published last year, researchers discovered that light exposure plays a crucial role in healing such defects, but also found that eliminating the lighting factor would bring back the same problem, resulting in a temporary fix. The new study, however, shows promising results. As part of the study, researchers made a perovskite-based solar device and exposed it to light, oxygen, and humidity levels between 40 to 50 percent, for 30 minutes, before it was completed. This action prevented the perovskite compound from degradation—which normally occurs in humid conditions. "When the light was applied, electrons bound with oxygen, forming a superoxide that could very effectively bind to electron traps and prevent these traps from hindering electrons," described the press release. "In the accompanying presence of water, the perovskite surface also gets converted to a protective shell. The shell coating removes traps from the surfaces but also locks in the superoxide, meaning that the performance improvements in the perovskites are now long-lived."