Fig. 4: Four phases of film formation during spin coating.
From: Out-of-equilibrium processes in crystallization of organic-inorganic perovskites during spin coating
Phase I: The thin film consists of colloidal precursors of photoinactive solid precursors (PbI2 and CH3NH3I) and liquid solvents (CH3)2N-HCO and (CH3)2SO. Nucleation of MAPI nanocrystals and conversion to phase II where the nanoparticles trimerize into thermodynamically stable orthorhombic solvent-complex of Pb3I8.2(CH3)2SO.2CH3NH3 with remainders of stable perovskite phase formed during nucleation. Phase III: Thermal decomposition of solvent-complex leading to the removal of plumboiodide coordinated solvent molecules at 100 °C from the thin film and the eventual dissolution-recrystallization of CH3NH3PbI3 from the film thickness. Phase IV: Perovskite crystallization complete and thermal ripening process of the thin film.
