Oral Presentation 26th ACMM “2020 Visions in Microscopy”

Advanced characterization of cesium lead halide and organolead halide perovskite nanocrystals at the atomic level (#95)

Eva Bladt 1 , Yu Tong 2 3 , Elke Debroye 4 , Haifeng Yuan 4 , Lakshminarayana Polavarapu 2 3 , Jochen Feldmann 2 3 , Maarten Roeffaers 5 , Johan Hofkens 4 , Sara Bals 1
  1. Electron Microscopy for Materials Science (EMAT), University of Antwerp, Antwerp, Belgium
  2. Nanosystems Initiative Munich (NIM), Munich, Germany
  3. Department of Physics and Center for NanoScience (CeNS), Chair for Photonics and Optoelectronics, Ludwig-Maximilians-Universität, Munich, Germany
  4. Department of Chemistry, KU Leuven, Leuven, Belgium
  5. Center for Surface Chemistry and Catalysis, KU Leuven, Leuven, Belgium

This talk focuses on the atomic-level investigation of two types of perovskites: CsPbX3 and CH3NH3PbX3 (X = Cl, Br, I) nanocrystals. The main challenge during these transmission electron microscopy (TEM) studies is to overcome electron beam-induced damage while imaging, as these materials are very sensitive to the electron beam.

CsPbX3 nanocubes are studied using high resolution HAADF-STEM and exit wave reconstruction to elucidate on their atomic structure and surface termination. The investigation of their surface termination is troublesome as the degradation of the structures starts at the edges of the cubes. A careful study revealed that the nanocrystals terminate with a Cs-I layer, which suggests that Cs-bound alkyl chains passivate them. Next, the use of HAADF-STEM confirmed the successful one-pot synthesis of CsPbX3 perovskite nanowires. By investigating different time steps, it was proven that these nanowires are formed through oriented attachment of the initially formed nanocubes. In addition, quantitative STEM is used to analyse local planar defects in CsPbX3 nanocrystals.

When investigation CH3NH3PbX3 nanocrystals, even more care is required, since they almost instantaneously change upon illumination. A time series of energy dispersive X-ray spectroscopy maps of a CH3NH3PbI3 nanocrystal shows a continuous decrease of the iodine peak. A combination of low-dose imaging and a template-matching procedure enabled us to reveal their crystal structure, before any deformation occurred. The perovskite lattice is clearly visible, which shows that the nanocrystals have a crystalline structure with a lattice parameter of ~6.4 Å.