Stability of Cs₂NaBiBr₆ and Cs₂NaBiCl₆

Area of Science:

• Materials Science
• Solid-State Chemistry
• Optoelectronics

Background:

• Lead-based perovskites are widely used in optoelectronics but raise toxicity concerns.
• Bismuth-based halide perovskites are explored as safer, non-toxic alternatives.
• Cesium sodium bismuth halides are a promising class of materials for optoelectronic applications.

Purpose of the Study:

• To synthesize and characterize cesium sodium bismuth halide thin films.
• To investigate the stability and structural properties of Cs2NaBiCl6 and Cs2NaBiBr6.
• To evaluate the potential of these materials as lead-free alternatives in optoelectronics.

Main Methods:

• Physical vapor deposition was used for thin film synthesis.
• X-ray diffraction (XRD) was employed for structural analysis.
• Optical band gap measurements were performed.

Main Results:

• Stable cubic Cs2NaBiCl6 thin films with a 3.4 eV band gap were successfully synthesized.
• Cs2NaBiBr6 was found to be unstable and dissociated into other phases.
• Similar XRD patterns for Cs3-xNaxBi2Br9 and Cs2NaBiBr6 challenge previous synthesis reports.

Conclusions:

• Cs2NaBiCl6 is a viable lead-free material for optoelectronic applications.
• The synthesis of Cs2NaBiBr6 requires further investigation due to observed instability.
• Careful characterization is crucial to confirm the formation of bismuth-based perovskites.