Raman Spectroscopy of Formamidinium-Based Lead Halide Perovskite Single Crystals

Raman spectroscopy is a powerful technique for the study of materials chemistry and nanostructure. This non-destructive technique is highly sensitive to molecular and crystal lattice vibrations, which allow for a comprehensive study of the vibrational modes of molecules incorporated in photovoltaic perovskite materials. In this study, we apply Raman spectroscopy to study FAPbX3 (X = Cl, Br, I) and FAxMA1-xPbI3 (FA stands for formamidinium; MA for methylammonium) metal halide perovskite single crystals and discuss the necessary conditions to obtain reliable data. We establish a correlation between perovskite composition and their unique Raman intensities/spectral shapes. In particular we identify that tuning of halide content results in a spectral shift of the organic features of the Raman spectrum due to changes in the strength of hydrogen bonding, while tuning of the organic cation is related more to changes in peak intensity. Moreover, the effect of temperature on the vibrational modes corresponding to ...