KIT: Vacuum coating of perovskite solar cells

The researchers' new method produces uniform perovskite layers even on structured silicon surfaces and achieved efficiencies of up to 24.3 percent. The results were published in the journal Nature Energy. "For industrial production, it is not only the efficiency that counts, but also whether a process is fast, robust and scalable," says Professor Ulrich Paetzold from KIT. The process used is based on close-space sublimation (CSS), in which the starting materials evaporate and react directly on the silicon cell to form a perovskite layer. "With close-space sublimation, we were able to apply even the demanding organic starting materials to silicon without solvents and in a short time," explains Sofia Chozas-Barrientos from the University of Valencia. In the experiment, the conversion was completed after just ten minutes.

Scalable production of perovskite-silicon tandem solar cells

To adjust the bandgap required for tandem solar cells, the researchers used a mixed organic source of methylammonium iodide and methylammonium bromide. "By controlling the ratio of these two components, we were able to control the bromine content in the finished material and achieve a bandgap of 1.64 electron volts," explains Dr. Alexander Diercks from KIT. Tests on smooth as well as nano- and microstructured silicon surfaces showed a uniform coating without adjusting the process parameters. The tandem solar cells produced achieved efficiencies of 23.5 to 24.3 percent. "The fact that close-space sublimation also produces uniform layers on structured silicon cells makes the approach relevant for practical applications," emphasizes Professor Henk Bolink from the University of Valencia.