Direct atomic scale characterization of the surface structure and planar defects in the organic-inorganic hybrid CH3NH3PbI3 by Cryo-TEM

The performance of halide perovskite solar cells is often dominated by structural defects. However, atomic scale characterization of the crystalline defects in organic–inorganic hybrid perovskites is hindered by the electron-beam sensitivity of the organic components in the structure. Here we reported the atomic scale characterization of CHNHPbI (MAPbI) single crystal using the state-of-the-art cryo-transmission electron microscopy. We confirm that the MAPbI structure is intact during high resolution cryo-TEM analysis by probing the content of carbon, nitrogen from the [CHNH]+ component using electron energy loss spectroscopy. Atomic steps of {200} surfaces were observed which shed light on the crystal growth details and low-energy surfaces. Surprisingly, high density of stacking faults are observed in the hybrid perovskite materials. We believe these fault structures serves the role of micro-interface between otherwise perfect lattices which facilitates charge separation and reduces the photon-generated carrier recombination within the crystal solids. First-principles calculations show that the presence of such stacking faults significantly changes the electronic structures of the materials, which may play a critical role in further optimizing the properties such as charge-carrier mobility, the carrier diffusion length and energy conversion efficiency of organic-inorganic hybrid perovskite-based energy harvesting devices.