Tunable Perovskite-Derived Bismuth Halides: Cs₃Bi₂(Cl_1-I)₉.

Area of Science:

• Materials Science
• Solid State Chemistry
• Optoelectronics

Background:

• Lead-based perovskites are widely used in optoelectronics but pose toxicity concerns.
• Bismuth-based perovskites are being explored as non-toxic alternatives.
• Previous research identified Cs₃Bi₂Cl₉, Cs₃Bi₂I₉, and Cs₃Bi₂Cl₃I₆.

Purpose of the Study:

• To investigate the structural and optical properties of Cs₃Bi₂(Cl_1-xI_x)₉ compounds.
• To understand the effect of varying iodine content (x) on the crystal structure and optoelectronic properties.
• To explore bismuth-based perovskites as safer alternatives to lead-based materials.

Main Methods:

• Powder and single-crystal X-ray diffraction to determine crystal structure.
• Optical absorption spectroscopy to study optical properties.
• Density functional theory (DFT) calculations for electronic structure analysis.

Main Results:

• All examined Cs₃Bi₂(Cl_1-xI_x)₉ compounds (x from 0.09 to 0.52) adopt the layered vacancy-ordered perovskite structure of Cs₃Bi₂Cl₃I₆.
• A small incorporation of iodine induces a structural switch to the Cs₃Bi₂Cl₃I₆ structure.
• Iodine atoms preferentially occupy capping sites on the BiX₆ octahedra.
• Optical absorption spectra show three main features, with the lowest-energy features red-shifting as iodine content (x) increases.

Conclusions:

• The Cs₃Bi₂(Cl_1-xI_x)₉ system readily forms layered vacancy-ordered perovskite structures.
• Iodine incorporation significantly influences the structure and optical properties of these bismuth-based perovskites.
• These findings contribute to the development of safer, tunable optoelectronic materials.