MIT Team 'Heals' Solar Cells With Intense Light

MIT researchers have found that light can "heal" flaws in some solar cells. The materials healed in the study are called perovskites, which can be used to create thin films with a number of electronic and optical properties that can be employed in solar cell applications.

Even though perovskites have the potential for solar cell applications, there are many tiny defects in their crystalline structure that can limit the process to convert light into electricity in a solar cell. The flaws are called traps and lead to electrons recombining with atoms before the cell harnesses the energy of their motion.

The study shows that intense illumination pushes iodide ions or atoms carrying an electric charge due to loss of an electron away from the light-saturated areas. This process carries the regional defects.

"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.

Even though this effect has been observed earlier, the current study is the first to show that the improvements in flaws are mainly due to the ions being pushed away by the illumination.

After finding ways to increase the effectiveness of perovskites by using light to heal them, the team works on maintaining the effect such that it becomes practical enough to become part of 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.