Scalable Synthesis of Micron Size Crystals of CH 3 NH 3 PbI 3 at Room Temperature in Acetonitrile via Rapid Reactive Crystallization

From application point of view, scalable, facile and rapid synthesis method for mass production of a homogeneous and phase pure CH 3 NH 3 PbI 3 micron size crystal at the industry level is still highly required, although it has been claimed that the CH 3 NH 3 PbI 3 crystals can be prepared by solution‐annealing the precursors at elevated temperature or prolonged reaction time. Herein, polycrystalline CH 3 NH 3 PbI 3 micron size crystals can be prepared by reactive crystallization of PbI 2 and CH 3 NH 3 I in a stoichiometric ratio at room temperature. TXM (Transmission X‐ray Microscopy), optical microscope, TEM and TEM‐EDX analysis were used to confirm the nature of the CH 3 NH 3 PbI 3 product. Moreover, Ostwald ripening of iodide ion into PbI 2 is proposed as the key step to form 3D PbI 3 − , followed by the intercalation of CH 3 NH 3 + for this reactive crystallization. Interestingly, this result suggests that industry level mass production of micron CH 3 NH 3 PbI 3 crystals is possible with this novel synthesis method.