Perovskite is poised to become a major material for solar cells, but before then it needs to overcome a major durability issue. Engineers at Princeton have unveiled a new perovskite solar cell design that tests suggest could last as long as 30 years of real-world use.

Silicon has been the go-to material for solar cells for decades, but in the last 15 years or so perovskites have been quickly catching up. They’re approaching the efficiency of silicon but are cheaper to make, lighter and more flexible.

The problem, however, is that perovskites aren’t very stable and tend to break down when exposed to the elements. Fixing that problem has been the focus of plenty of past work, with scientists experimenting with adding bulky molecules, old pigments or quantum dots.

In the new study, the Princeton team addressed the stability issue by adding an ultra-thin capping layer between the light-absorbing perovskite layer and the charge-carrying layer. Just a few atoms thick, this capping layer was made of carbon disulfide, lead, iodine and chlorine, and served to protect the device from burning out within a few weeks.

Other teams have added 2D layers to extend the lifespan of perovskite solar cells, but not to the degree of this new one. By the team’s estimate, perovskite solar cells made with this capping layer could last up to 30 years of outdoor operation, making it the first of its type to cross the commercial threshold of a 20-year lifetime.