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BiOBr Surface-Functionalized Halide Double-Perovskite Films for Slow Ion Migration and Improved Stability
Bhawna1, Mrinmoy Roy1, Amandeep Kaur1
1Indian Institute of Technology Bombay, Mumbai, Maharashtra 400076, India.
ACS Applied Materials & Interfaces
|March 28, 2023
Summary
This study demonstrates thermal diffusion of halide ions in lead-free double-perovskite thin films. Annealing Cs2AgBiBr6 and Cs2AgBiCl6 films activates ion migration, forming mixed phases and confirming film stability.
Area of Science:
- Materials Science
- Solid-state Chemistry
- Perovskite Optoelectronics
Background:
- Lead-free halide double-perovskites (Cs2AgBiX6) are promising for optoelectronic applications.
- Understanding ion migration is crucial for device stability and performance.
Purpose of the Study:
- To investigate the thermal diffusion of halide ions in surface-tailored Cs2AgBiX6 thin films.
- To analyze the impact of annealing on ion migration and film composition.
Main Methods:
- Physical stacking of Cs2AgBiBr6 and Cs2AgBiCl6 thin films.
- Annealing at temperatures ranging from room temperature to 150 °C.
- Characterization using absorption spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS).
Main Results:
- Observed color changes and spectral shifts (redshift/blueshift) indicating Br- and Cl- ion migration.
- Formation of mixed halide phases (Cs2AgBiClxBr6-x) confirmed by XRD and XPS.
- Calculated activation energies for bromide (0.42 eV) and chloride (0.35 eV) ion mobility.
Conclusions:
- Confirmed thermal diffusion of halide ions in Cs2AgBiX6 thin films.
- Identified a BiOBr passivation layer potentially slowing ion diffusion.
- Demonstrated the stability and high quality of the double-perovskite films due to slow ion migration.
