Perovskite Crystallization Dynamics during Spin-Casting: An Wide-Angle X-ray Scattering Study.

wide-angle X-ray scattering (WAXS) has been measured during the spin coating process used to make the precursor films required for the formation of thin films of perovskite. A customized hollow axis spin coater was developed to permit the scattered X-rays to be collected in transmission geometry during the deposition process. Spin coating is the technique most commonly used in laboratories to make thin perovskite films. The dynamics of spin-casting MAPbI Cl and FAPbI Cl films have been investigated and compared to investigate the differences between the dynamics of MAPbI Cl and FAPbI Cl film formation. In particular, we focus on the crystallization dynamics of the precursor film formation. When casting MAPbI Cl , we observed relatively fast 1D crystallization of the intermediate product MAPbICl. There was an absence of the desired perovskite phase formed directly; it only appeared after an annealing step that converted the MAPbICl to MAPbI. In contrast, slower crystallization via a 3D precursor was observed for FAPbI Cl film formation compared to MAPbI Cl . Another important finding was that some FAPbI Cl perovskite was generated directly during spin-casting before annealing. These findings indicate that there are significant differences between the crystallization pathways for these two perovskite materials. These are likely to explain the differences in the lifetimes of the resulting perovskite solar cell devices produced using FA and MA cations.