Ellipsometry - Principles and Techniques for Materials Characterization || Spectroscopic Ellipsometry Study of Organic-Inorganic Halide: FAPbIxBr3?x Perovskite Thin Films by Two-Step Method

摘要： Spectroscopic ellipsometry (SE) was used to investigate the role of isopropyl alcohol (IPA) solvent in the synthesis of organic-lead-halide perovskite CH(NH2)2PbIxBr3?x [FAPbIxBr3?x] thin films including the effect of I/Br composition ratio by the two-step reaction of an amorphous (a-)PbIxBr2?x layer and FAIxBr1?x solution diluted in IPA. An optical dispersion model was developed to extract the complex refractive index N (=n + ik), optical transition, and film thickness of FAPbIxBr3?x perovskites by SE analysis at different I/Br composition ratio as a function of immersion time in a solution of FAIxBr1?x diluted in IPA. SE combined with X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) revealed that Br incorporation into films promoted the densification of FAPbIxBr3?x perovskite network along with increased film thickness and volume fraction of void. IPA promoted film crystallization of a-PbIxBr2?x accompanied by the formation of surface roughness, grain boundaries, and voids, followed by enhanced diffusion of FAIxBr1?x into the grain boundaries/voids in the mesoporous crystallized PbIxBr2?x network. These processes contribute synergistically to the growth of the perovskite structure.