Local Structure of Multinary Hybrid Lead Halide Perovskites Investigated by Nuclear Quadrupole Resonance Spectroscopy

Abstract

Hybrid organic–inorganic lead halide perovskites have emerged as popular low-cost, solution-processable semiconductors owing to their outstanding optical and electronic characteristics. The structural characterization of these soft solids has proven challenging due to increased structural dynamics and static disorder. Nuclear quadrupole resonance (NQR) may serve as a powerful tool for probing the local structure of the halide anions in bulk and nanocrystalline forms of these perovskites. Here, we characterize the atomic structure of mixed-cation and mixed-anion solid solutions derived from cubic formamidinium lead iodide (FAPbI3), typically used in photovoltaics and photodetectors, using 127I NQR. Even minute quantities of Cs ions on FA sites or Br ions on I sites lead to a multitude of different local environments, readily seen by NQR spectroscopy. At 10% Cs, signatures of Cs-ion clustering arise, pointing to the onset of the phase separation, observed by diffraction methods at higher Cs contents. On the contrary, Br-ion distribution appears homogeneous across all Br-to-I ratios. We anticipate that halide NQR studies will be indispensable for understanding the atomistic structure of diverse multinary metal halides, also in their diverse forms—from single crystals to thin films and nanocrystals.