The understanding of electronic behaviour at grain boundaries is crucial in designing hybrid perovskite materials, which have promising applications in solar cells and light-emitting diodes. Specifically, charge trap sites at grain boundaries need to be identified in order to optimise synthesis processes. In this work we combine several electron microscopy techniques, including Scanning Electron Diffraction (SED) and Energy Dispersive X-ray (EDX) spectroscopy, with optical analyses to correlate the nanoscale optoelectronic properties with local chemical composition and crystal structure. Our combined results show that deep photo-excited hole traps form at the interfaces between pristine grains with balanced halide distributions and cubic structure, and grains that are compositionally inhomogeneous with a distorted structure. Thus, passivation and film growth strategies that target the removal of these inhomogeneous and distorted grains will be critical to eliminate performance losses and instabilities.

Figure: Comparison of two grains in a perovskite film, showing differences in bromine content and local electron diffraction data.