Oral Presentation 26th ACMM “2020 Visions in Microscopy”

Illuminating the origin of the "zero-dimentional perovskite" phase in Cs4PbBr6 (#98)

Mark N Lockrey 1 , Nicolas Riesen 2 3 , Kate Badek 4 , Hans Riesen 4
  1. Microstructural Analysis Unit, University of Technology Sydney, Sydney, New South Wales, Australia
  2. Institute for Photonics and Advanced Sensing and School of Physical Sciences, The University of Adelaide, Adelaide, South Australia, Australia
  3. University of South Australia and Future Industries Institute, Mawson Lakes, South Australia, Australia
  4. School of Science, The University of New South Wales, Canberra, Australian Capital Territory, Australia

There is great interest in the use of highly-efficient all-inorganic halide perovskites CsnPbBr2+n for optoelectronic applications due to their size-tunable bandgaps, superb quantum efficiencies and increased stability over inorganic peroviskites. However, there is considerable debate over the origins of the green luminescence, with reports suggesting that it originates from either from defects in the Cs4PbBr6 lattice or CsPbBr3 impurities/inclusions. There are reports of an interesting zero-dimensional perovskite phase Cs4PbBr6 which crystallizes in the (167) space group, where the PbBr6 octahedra are isolated. The isolation of the octahedra allows for interesting photophysical properties because of strong quantum confinement and strong exciton-phonon interactions. In contrast, the CsPbBr3 perovskite crystallizes with corner sharing PbBr6 octahedra. The latter is the main structural feature that makes CsPbBr3 a relatively narrow band-gap semiconductor.


Cs4PbBr6 was prepared by ball-milling stoichiometric mixtures of CsBr (0.4256 g) and PbBr2 (0.1835 g) on a Retsch mixer mill at 20 Hz for 90 minutes. The product was then transferred into a petri dish and dried at 50 oC for 30 min with subsequent ball-milling for another 90 min. Cathodoluminescence measurements were performed on a FEI Verios 460 SEM equipped with a Gatan MonoCL4 Elite CL detection system. Full spectral maps were collected using a beam voltage of 5 kV and a current of 200 pA, at room temperature. EDX measurements were collected on the same microscope using an Oxford EDX detector and processed using Aztec.


Cathodoluminescence imaging clearly shows the presence of small crystals embedded in/or between larger crystallites of Cs4PbBr6 and they emit around 520 nm. EDX shows that the smaller crystal inclusions have a Pb:Br ratio that is approximately 2 times higher, confirming the CsPbBr3 phase. These measurements make significant inroads into understanding these lead halide perovskites for their use in a variety of optoelectronic and photovoltaic applications.