GIWAXS Analysis on Preferred Orientation in Metal Halide Perovskite Films Via Alkylamines

We investigated the effects of the alkyl chain length of alkylamine ligands (AALs), known to modify metal halide perovskite crystallites, on the preferential alignment of the CsFAMA crystal domains using two-dimensional grazing incidence wide-angle X-ray scattering (2D GIWAXS) measurements at various incident angles. In the absence of AALs, most (100) perovskite crystals were tilted 45 degrees from the surface normal; the ratio of the 45 degrees-tilted to isotropically oriented (100) crystals was similar in both the surface and bulk regions. However, in the presence of AALs, the 45 degrees-tilted (100) crystals decreased, while the isotropically oriented (100) crystals increased, in both regions. In addition, vertically oriented (100) crystals were formed in the presence of AALs, which were observed only in the surface region of AALs with short alkyl lengths. As the alkyl chain length increased, vertically oriented (100) crystals appeared in both the surface and bulk regions of the film, i.e., the whole region of the film.