Three-dimensional
hybrid organic–inorganic perovskites with
halide, formate, or hypophosphite ligands are promising photovoltaic,
light-emitting, and multiferroic materials. Since the properties of
these compounds are strongly affected by changes in lattice dynamics,
it is of great importance to understand their phonon properties. We
report Raman and IR spectra for a number of perovskites to understand
the effect of various metal-linker frameworks on vibrations of methylhydrazinium,
formamidinium, and methylammonium cations as well as effects of these
cations on lattice phonons in lead bromide analogues. Our results
show that the lattice dynamics and energy of lattice phonons of lead
halides depend strongly on the type of organic cation and temperature.
In particular, at room temperature, the dynamics of methylhydrazinium
cations is much slower compared to the dynamics of methylammonium
and formamidinium cations, implying weaker electron scattering in
the former case and thus significantly different optoelectronic properties
compared to the formamidinium and methylammonium analogues. We also
show that the size of the halide ion affects the energy of internal
modes, but this effect is much more pronounced when halide ligands
are replaced by formate or hypophosphite anions, especially in the
case of formamidinium analogues. We attribute this behavior to strong
variation of hydrogen bond strength and changes in the internal structure
of organic cations.