Reaction Dynamics of C(NH2)3SnI3 Formation from Vacuum-Deposited C(NH2)3I and SnI2 Bilayer Thin Films Investigated by In Situ Infrared Multiple-Angle Incidence-Resolved Spectroscopy

Understanding the formation process of organic-inorganic halide perovskite (OIHP) thin films is important for the fabrication of high-quality thin films, which, in turn, are crucial for achieving high-performance devices. To address this challenge, we developed an in situ system of infrared multiple-angle incidence-resolved spectroscopy (IR-MAIRS) combined with a vacuum deposition system. "Orientation-free" isotropic spectra constructed from IR-MAIRS spectra enable us to perform quantitative analysis of the formation process of C(NH₂)₃SnI₃ (GASnI₃) thin films from unreacted C(NH₂)₃I (guanidine hydroiodide (GAI))/SnI₂ bilayer structures predeposited in a vacuum. The analysis of the dependence of the GASnI₃ formation rate on the reaction temperature using the Avrami model has revealed that a diffusion-controlled reaction process of GAI and SnI₂ governs the formation kinetics. The present study points to the usefulness of in situ IR-MAIRS analysis in understanding the growth mechanisms of vacuum-deposited OIHP thin films and hence the potential to accelerate the development of vacuum processes for the fabrication of high-quality OIHP thin films.