Determination of the True Lateral Grain Size in Organic–Inorganic Halide Perovskite Thin Films

Abstract

In this letter, methylammonium lead iodide (MAPbI3) thin films were examined via piezoresponse force microscopy (PFM) and nanoindentation (NI) to determine if long-range atomic order existed across the full width and depth of the apparent grains. From the PFM, the piezoelectric response of the films was strongly correlated with low-index planes of the crystal structure and ferroelastic domains in macroscale solution-grown MAPbI3 crystals, which implied long-range order near the top surface. From the NI, it was found that the induced cracks were straight and extended across the full width of the apparent grains, which indicated that the long-range order was not limited to the near-surface region, but extended through the film thickness. Interestingly, the two MAPbI3 processes examined resulted in subtle differences in the extracted electro-mechanical and fracture properties, but exhibited similar power conversion efficiencies of >17% in completed devices.

First-Principles Study of Ferroelastic Twins in Halide Perovskites

“…We found both ferroelastic twins to be polar; a result that has not been discussed in their observation [1,17,26,27,[44][45][46][47]. The layer-by-layer polarisation P was determined using Born effective charges computed in the centrosymmetric P m 3m structure [48].…”

Evolution of ferroelectric domains in methylammonium lead iodide and correlation with the performance of perovskite solar cells

“…[22,24] The effects occurring in a ferroelectric semiconductor must not be confused with the bulk-photovoltaic effect which only occurs in dielectrics. [25,26] Although controversial discussions surrounding the ferroelectric or non-ferroelectric nature of MAPbI 3 continue to fill the scientific literature, [27][28][29][30][31][32][33] the authors of this study consider the comprehensive set of experimental findings compelling in favor of ferroelectricity. So far, no other theory can explain all of the observed domain and material properties.…”

Spatial Inhomogeneity of Methylammonium Lead-Mixed Halide Perovskite Examined by Space- and Time-Resolved Microwave Conductivity

“…The diffusion length of charge carriers has been reported to be 1 μm in Cl-doped MAPbI 3 (ref (14)) and 50–175 μm in single-crystal MAPbI 3 (refs (15, 49)), whereas the grain size of solution-processed multicrystalline MAPbI 3 is typically a few hundreds of nanometers to several micrometers. 50 Therefore, one point in the map (∼20 μm spot and 200 μm step) includes multiple grains that are different from a neighboring point. An intergrain charge transport is critical to a long-range mobility; 51 however, the present STRMC is unable to resolve the electronic properties of the grain interface.…”