Berkeley Lab

Double perovskite nanocrystals and watching the structure formation of solution-cast perovskite films

By Greg Su

Double perovskites are promising forms that may help address issues of lead toxicity in standard perovskite structures. Jakob Dahl from UC Berkeley reported on the synthesis of lead-free double perovskite nanocrystals of the form Cs2AgMX6. These nanocrystals can be made down to 10 nanometers in size. At these size scales, quantum confinement effects can become significant. However, Jakob showed that although results from certain measurements can be misleading, these nanocrystals do not show signs of quantum confinement. Furthermore, a titration assay was used to access double perovskite stability, and stability depends on the metals used, with decreasing stability seen forĀ Cs2AgInCl6, Cs2AgBiCl6, and Cs2AgSbCl6, respectively. This is important for understanding stability trends of perovskites in general.

Perovskites can be solution-processed allowing for large-area deposition. However, this is a dynamic process that is challenging to monitor in real-time. Shambavi Pratap from the Technical University of Munich has been working at the Advanced Light Source through an ALS Doctoral Fellowship to develop a custom-made sample chamber that is capable of tracking the crystallinity of perovskite films during spin-coating, addition of an antisolvent, and solvent evaporation. This is used at beamline 12.3.2 at the ALS, and can be transferred to other beamlines as well. Her results show that an intermediate crystal phase forms right after addition of the anti solvent before the final crystalline phase that persists after solvent evaporation. Overall, these capabilities allow for new insights into the processes that dictate the evolution of these important photovoltaic materials.