  Organic-inorganic hybrid perovskites (OIHPs) have attracted extensive
research interest as a promising candidate for efficient and inexpensive solar
cells. Transmission electron microscopy characterizations that can benefit the
fundamental understanding and the degradation mechanism are widely used for
these materials. However, their sensitivity to the electron beam illumination
and hence structural instabilities usually prevent us from obtaining the
intrinsic information or even lead to significant artifacts. Here, we
systematacially investigate the structural degradation behaviors under
different experimental factors to reveal the optimized conditions for TEM
characterizations of OIHPs by using low-dose electron diffraction and imaging
techniques. We find that a low temperature does not slow down the beam damage
but instead induces a rapid amorphization for OIHPs. Moreover, a less severe
damage is observed at a higher accelerating voltage. The beam-sensitivity is
found to be facet-dependent that a (100) exposed MAPbI3 surface is more stable
than (001) surface. With these guidance, we successfully acquire the atomic
structure of pristine MAPbI3 and identify the characterization window that is
very narrow. These findings are helpful to guide future electron microscopy
characterization of these beam-sensitive materials, which are also useful for
finding strategies to improve the stability and the performance of the
perovskite solar cells.
