Nanoscale Mapping of Bromide Segregation on the Cross Sections of Complex Hybrid Perovskite Photovoltaic Films Using Secondary Electron Hyperspectral Imaging in a Scanning Electron Microscope.

Mixed halide (I/Br) complex organic/inorganic hybrid perovskite materials have attracted much attention recently because of their excellent photovoltaic properties. Although it has been proposed that their stability is linked to the chemical inhomogeneity of I/Br, no direct proof has been offered to date. Here, we report a new method, secondary electron hyperspectral imaging (SEHI), which allows direct imaging of the local variation in Br concentration in mixed halide (I/Br) organic/inorganic hybrid perovskites on a nanometric scale. We confirm the presence of a nonuniform Br distribution with variation in concentration within the grain interiors and boundaries and demonstrate how SEHI in conjunction with low-voltage scanning electron microscopy can enhance the understanding of the fundamental physics and materials science of organic/inorganic hybrid photovoltaics, illustrating its potential for research and development in "real-world" applications.