New research shows that the next generation of technology in solar cells could actually be healed when damaged by, well, light and a little bit of humidity. That’s what new research into perovskite crystals is showing.
Perovskite crystals are already one of the most promising materials for the next generation of solar cells and panels. They’re cheap to manufacture and produce and in half a decade of research have showed they’re capable of efficiency levels close to that of silicon-based solar cells—if not exceed them.
Now an international team of researchers from Cambridge, MIT, Oxford, Bath and Delft universities have shown that defects in perovskite solar cells can be permanently healed and published their work in the inaugural edition of the journal Joule, published by Cell Press. "In perovskite solar cells and LEDs, you tend to lose a lot of efficiency through defects," said Dr Sam Stranks, who led the research while he was a Marie Curie Fellow jointly at MIT and Cambridge. "We want to know the origins of the defects so that we can eliminate them and make perovskites more efficient."
The problem with perovskites are that they are often delicate and there are small defects in their crystalline structure called traps in which electrons can get "stuck" before their energy is harnessed. When electrons are trapped in the crystals defects the material is less efficient at converting sunlight into electricity.
Stranks and the group of international researchers had shown in 2016 that defects in perovskite structures could be healed with exposure to light as it forced iodide ions to migrate from a lit part of a perovskite solar cell, but the effects were temporary as the ions returned when the light source was removed. Now they have shown a method to permanently fix such deficiencies.
This time around they printed a perovskite-based device using techniques compatible with roll-to-roll processes. But before completing manufacturing the device they exposed it to light, oxygen and humidity levels between 40 and 50 percent for 30 minutes. After that they deposited other layers to finish the device.
"It's counter-intuitive, but applying humidity and light makes the perovskite solar cells more luminescent, a property which is extremely important if you want efficient solar cells," said Stranks, who is now based at Cambridge's Cavendish Laboratory. "We've seen an increase in luminescence efficiency from 1 percent to 89 percent, and we think we could get it all the way to 100 percent, which means we could have no voltage loss—but there's still a lot of work to be done."
The researchers found that when light was applied, electrons bound with oxygen. That formed a superoxide that bounded to the electron traps preventing them from hindering electrons. The presence of water converted the perovskite surface into a protective shell that removed traps from the surfaces while locking in the superoxide, creating long-lived performance improvements in the perovskites.Tweet