Vibrational study of lead bromide perovskite materials with variable cations based on Raman spectroscopy and density functional theory

Metal halide-based perovskite semiconductors exhibit excellent optoelectronic properties such as a sharp absorption edge, high absorption coefficients, and a small recombination rate. Mixed compositions result in a variation of the structure of these perovskite materials, which also influences their electronic properties. Even though huge progress in synthesis and device fabrication has been made, still systematic investigations of structural properties of lead halide-based perovskites are missing. Here, we systematically investigate the vibrational features of lead bromide-based perovskites using Raman spectroscopy and density functional theory (DFT). We have performed these investigations using MA(+), FA(+), and Cs+ as cations in the lead bromide structures and determined the vibrational modes both from Raman experiments and DFT simulations. We find a clear dependence of the Raman band wavenumbers on the chosen cations. The structural differences are reflected in the different line-width broadening of Raman bands, charge distribution on the cations and the extent of their interactions with the bromide anions.