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Title: Thin-film preparation and characterization of Cs 3Sb 2I 9: A lead-free layered perovskite semiconductor

In this study, computational, thin-film deposition and characterization approaches have been used to examine the ternary halide semiconductor Cs 3Sb 2I 9. Cs 3Sb 2I 9 has two known structural modifications, the 0-D dimer form (space group P6 3/mmc, No. 194) and the 2-D layered form (P$$\bar{3}$$ m1, No. 164), which can be prepared via solution and solid state or gas phase reactions, respectively. Our computational investigations suggest that the layered form, which is a one-third Sb-deficient derivative of the ubiquitous perovskite structure, is a potential candidate for high-band-gap photovoltaic (PV) applications. In this work, we describe details of a two-step deposition approach that enables the preparation of large grain (>1 µm) and continuous thin films of the lead-free layered perovskite derivative Cs 3Sb 2I 9. Depending on the deposition conditions, films that are c-axis oriented or randomly oriented can be obtained. The fabricated thin films show enhanced stability under ambient air, compared to methylammonium lead (II) iodide perovskite films stored under similar conditions, and an optical band gap value of 2.05 eV. Photoelectron spectroscopy study yields an ionization energy of 5.6 eV, with the valence band maximum approximately 0.85 eV below the Fermi level, indicating near-intrinsic, weakly p-type character. Density Functional Theory (DFT) analysis points to a nearly direct band gap for this material (less than 0.02 eV difference between the direct and indirect band gaps) and a similar high-level of absorption compared to CH 3NH 3PbI 3. The photoluminescence peak intensity of Cs 3Sb 2I 9 is substantially suppressed compared to that of CH 3NH 3PbI 3, likely reflecting the presence of deep level defects that result in non-radiative recombination in the film, with computational results pointing to I i, IS b, and V I as being likely candidates. A key further finding from this study is that, despite a distinctly layered structure, the electronic transport anisotropy is less pronounced due to the high ionicity of the I atoms and the strong anti-bonding interactions between the Sb s lone pair states and I p states, which leads to a moderately dispersive valence band.
 [1] ;  [2] ;  [3] ;  [1] ;  [4] ;  [3] ;  [3] ;  [4] ;  [1]
  1. Duke Univ., Durham, NC (United States)
  2. The Univ. of Toledo, Toledo, OH (United States); Shanghai Univ., Shanghai (China)
  3. Dalhousie Univ., Halifax, NS (Canada)
  4. The Univ. of Toledo, Toledo, OH (United States)
Publication Date:
Grant/Contract Number:
Published Article
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 27; Journal Issue: 16; Journal ID: ISSN 0897-4756
American Chemical Society (ACS)
Research Org:
Duke Univ., Durham, NC (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1222454