Time-Resolved Orientation and Phase Analysis of Lead Halide Perovskite Film Annealing Probed by In Situ GIWAXS

Scalable thin-film deposition methods are increasingly important for hybrid lead halide perovskite thin films. Understanding the structure evolution during non-equilibrium processes helps to find suitable materials and processing parameters to produce films with well-performing optoelectronic properties. Here, spin-cast and slot-die coated bilayers of lead iodide (PbI₂) and methylammonium iodide (MAI) are investigated by in situ grazing-incidence wide-angle X-ray scattering during the thermal annealing process, which converts the bilayer into methylammonium lead iodide (MAPI). Photoluminescence (PL) and UV/Vis measurements show increasing crystallinity during the annealing process and a slight PL red-shift of the spin-cast film, attributed to crystallite coalescence that is not prominent for the slot-die coated film. The disintegration of the solvent-precursor complex (MA)₂(Pb₃I₈) ⋅ 2 DMSO and conversion into perovskite are followed in situ and differences in the morphology and time evolution are observed. In both, spin-cast and slot-die coated thin-films, the isotropic orientation is dominant, however, in the slot-die coated films, the perovskite crystallites have an additional face-on orientation ((110) parallel to substrate) that is not detected in spin-cast films. An Avrami model is applied for the perovskite crystal growth that indicates reduced dimensionality of the growth for the printed thin films.