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 CH3NH3PbI3 (MAPbI(3)) single crystal using the state-of-the-art cryo-transmission electron microscopy. We confirm that the MAPbI(3) structure is intact during high resolution cryo-TEM analysis by probing the content of carbon, nitrogen from the [CH3NH3]+ component using electron energy loss spectroscopy. Atomic steps of {200}(T) 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.