Direct Correlation between Local Stoichiometry and Optoelectronic Properties in CH3NH3PbI3 Films

As solution-processed organic-inorganic perovskite solar cells continue to climb, reports of device instability and variability have motivated fundamental studies of microscale inhomogeneities in these materials. In this work, we study device-relevant CH3NH3PbI3 perovskite films using cathodoluminescence in scanning transmission electron microscopy in conjunction with energy dispersive X-ray spectroscopy to directly correlate local stoichiometric fluctuations with spatial variations in cathodoluminescence intensity. Further, we observe the emergence of localized large bandgap regions in the CH3NH3PbI3 films attributed to electron beam-induced iodide redistribution, which may reflect the impacts of ion migration during device operation. This work demonstrates the fundamental impacts of ion migration/segregation on local optoelectronic properties of organic-inorganic perovskite films.