A team of MIT researchers has discovered that light can "heal" defects in certain solar cells. The materials healed in the study are perovskites, which can be used to create thin films with numerous electronic and optical properties and have the potential to be used in solar cell applications.
Although perovskites possess plenty of potential for solar cell applications, tiny defects in their crystalline structure can hinder the process that converts light into electricity in a solar cell. These defects, referred to as traps, cause electrons to recombine with atoms before the cell can harness the energy of their motion.
The current study reveals that intense illumination pushes the iodide ions - atoms that carry an electric charge due to loss of an electron - away from the light-saturated region, and in the process brings all of the regional defects with them.
"This is the first time this has been shown, where just under illumination, where no [electric or magnetic] field has been applied, we see this ion migration that helps to clean the film. It reduces the defect density," said Samuel Stranks of MIT and senior author of the study.
Previous research has observed this effect before, but the current study is the first to show that the improvement in defects is caused by the ions being pushed away by the illumination.
Now that the team has discovered a way of increasing the effectiveness of perovskites by using light to heal them, the team is working on maintaining the effect to a degree that makes it practical enough to integrate into commercial applications.
"I think the paper provides valuable insight that is likely to help people make more efficient solar cells by figuring out how to reduce the number of iodine vacancies," said Michael McGehee of Stanford University, who was not involved in the study. "I think it is fascinating that illuminating the perovskites improves their photoluminescence efficiency by enabling iodine to move around and eliminate iodine vacancies.
"This research does not make solar cells better, but it does greatly increase our understanding of how these complex materials function in solar cells," he added.
The findings were published in the May 24 issue of Nature Communications.
