Microscopic (Dis)order and Dynamics of Cations in Mixed FA/MA Lead Halide Perovskites

Recent developments in the field of high efficiency perovskite solar cells are based on stabilization crystal structure FAPbI3 while preserving its excellent optoelectronic properties. Compositional engineering of, for example, MA or Br mixed into results desired effects, but detailed knowledge local structural features, such as (dis)order cation interactions formamidinium (FA) and methylammonium (MA), is still limited. This is, however, crucial their further development. Here, we shed light microscopic distribution FA perovskites MA1–xFAxPbI3 MA0.15FA0.85PbI2.55Br0.45 by combining high-resolution double-quantum 1H solid-state nuclear magnetic resonance (NMR) spectroscopy with state-of-the-art near-first-principles accuracy molecular dynamics (MD) simulations using machine-learning force-fields (MLFFs). We show that a small scale, partial clustering takes place over whole MA/FA compositional range. A reasonable driving force might be an increase dynamical freedom cations FA-rich regions. While displays similar ordering systems, average cation–cation interaction strength increased significantly this double material, indicating restriction space accessible to immobilization upon Br– incorporation. Our heterogeneities composition halide perovskites, helping exploit full potential.