From 0D Cs 3 Bi 2 I 9 to 2D Cs 3 Bi 2 I 6 Cl 3: Dimensional Expansion Induces a Direct Band Gap but Enhances Electron-Phonon Coupling

Kyle M. McCall, Constantinos C. Stoumpos, Oleg Y. Kontsevoi, Grant C.B. Alexander, Bruce W. Wessels, Mercouri G. Kanatzidis*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

49 Scopus citations


Alternative all-inorganic halide perovskites are sought to replace the hybrid lead halide perovskites because of their increased stability. Here, the (111)-oriented defect perovskite family A 3 M 2 X 9 based on trivalent M 3+ is expanded through the use of mixed halides, resulting in Cs 3 Bi 2 I 6 Cl 3 . This compound shares the (111)-oriented 2D bilayer structure of α-Cs 3 Sb 2 I 9 (space group P3..m1), with Cl occupying the bridging positions of the bilayers and I in the terminal sites, in contrast to the parent compound Cs 3 Bi 2 I 9 , which consists of 0D molecular [Bi 2 I 9 ] 3- dimers. The increased dimensionality induces a direct band gap as calculated by density functional theory but has an absorption edge of 2.07 eV, nearly identical to the indirect band gap compound Cs 3 Bi 2 I 9 . Intriguingly, there is a remarkable lack of Cl orbital contribution to the band edge states of Cs 3 Bi 2 I 6 Cl 3 , despite Bi-Cl bonds binding all octahedra together. This highlights the importance of interlayer interactions in the defect perovskite family, which enhances the effective dimensionality of these 2D and 0D materials and may improve their optoelectronic performance. However, these changes in the excitonic absorption do not reflect free excitons, as Cs 3 Bi 2 I 6 Cl 3 exhibits broad photoluminescence as a result of self-trapped excitons, which appear to be universal in the (111)-oriented defect perovskites.

Original languageEnglish (US)
Pages (from-to)2644-2650
Number of pages7
JournalChemistry of Materials
Issue number7
StatePublished - Apr 9 2019

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry


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