Preferred crystallographic orientation in polycrystalline
films
is desirable for efficient charge carrier transport in metal halide
perovskites and semiconductors. However, the mechanisms that determine
the preferred orientation of halide perovskites are still not well
understood. In this work, we investigate crystallographic orientation
in lead bromide perovskites. We show that the solvent of the precursor
solution and organic A-site cation strongly affect the preferred orientation
of the deposited perovskite thin films. Specifically, we show that
the solvent, dimethylsulfoxide, influences the early stages of crystallization
and induces preferred orientation in the deposited films by preventing
colloidal particle interactions. Additionally, the methylammonium
A-site cation induces a higher degree of preferred orientation than
the formamidinium counterpart. We use density functional theory to
show that the lower surface energy of the (100) plane facets in methylammonium-based
perovskites, compared to the (110) planes, is the reason for the higher
degree of preferred orientation. In contrast, the surface energy of
the (100) and (110) facets is similar for formamidinium-based perovskites,
leading to lower degree of preferred orientation. Furthermore, we
show that different A-site cations do not significantly affect ion
diffusion in bromine-based perovskite solar cells but impact ion density
and accumulation, leading to increased hysteresis. Our work highlights
the interplay between the solvent and organic A-site cation which
determine crystallographic orientation and plays a critical role in
the electronic properties and ionic migration of solar cells.