Researchers from the University of Science and Technology of China, Hefei National Research Center for Physical Sciences at the Microscale, Chinese Academy of Sciences and University of Colorado (CU Boulder) have reported an innovative method to manufacture perovskite solar cells.
A major challenge in commercializing perovskite solar cells at a commercial scale is the process of coating the semiconductor onto the glass plates which are the building blocks of panels. Currently, the coating process has to take place in a small box filled with non-reactive gas, such as nitrogen, to prevent the perovskites from reacting with oxygen, which decreases their performance. “This is fine at the research stage. But when you start coating large pieces of glass, it gets harder and harder to do this in a nitrogen filled box,” said Michael McGehee, a professor in the Department of Chemical and Biological Engineering and fellow with CU Boulder’s Renewable & Sustainable Energy Institute.
McGehee and his collaborators set off to find a way to prevent that damaging reaction with the air. They found that adding dimethylammonium formate, or DMAFo, to the perovskite solution before coating could prevent the materials from oxidizing. This discovery enables coating to take place outside the small box, in ambient air. Experiments showed that perovskite cells made with the DMAFo additive can achieve an efficiency of nearly 25% on their own, comparable to the current efficiency record for perovskite cells of 26%. The additive also improved the cells’ stability.
Commercial silicon panels can typically maintain at least 80% of their performance after 25 years, losing about 1% of efficiency per year. Perovskite cells, however, are more reactive and degrade faster in the air. The new study showed that the perovskite cell made with DMAFo retained 90% of its efficiency after the researchers exposed them to LED light that mimicked sunlight for 700 hours. In contrast, cells made in the air without DMAFo degraded quickly after only 300 hours.
While this is a very encouraging result, longer tests are needed to determine how these cells hold up overtime. “It’s too early to say that they are as stable as silicon panels, but we're on a good trajectory toward that,” McGehee said.
At the same time, McGehee’s team is actively developing tandem cells with a real-world efficiency of over 30% that have the same operational lifetime as silicon panels.