Halide Ion Exchange Mechanisms in 2D Ruddlesden-Popper Perovskites: Diffusion- vs Reaction-Limited

Area of Science:

• Materials Science
• Solid-State Chemistry
• Optoelectronics

Background:

• Halide ion exchange is crucial for tuning perovskite optoelectronic properties.
• The mechanistic understanding of halide ion migration in 2D perovskites lags behind 3D counterparts.
• The specific impact of spacer ligand structure on halide ion mobility in 2D perovskites remains unclear.

Purpose of the Study:

• To investigate the role of spacer ligand structure in halide ion mobility within 2D perovskites.
• To elucidate the mechanisms governing halide ion exchange in 2D perovskite systems.
• To determine the halide ion diffusion coefficients influenced by ligand properties.

Main Methods:

• Physically pairing 2D bromide and iodide perovskite films.
• Applying thermal stress to induce halide ion migration.
• Tracking absorption changes to monitor ion movement.
• Calculating halide ion diffusion coefficients.

Main Results:

• Thermally driven bidirectional halide ion movement was observed in 2D perovskite films.
• Halide ion diffusion coefficients were determined and found to be dependent on spacer ligand type (aliphatic vs. aromatic) and glass transition temperature (Tg).
• Different exchange mechanisms and kinetic intermediates (heterogeneous vs. homogeneous alloying) were identified based on ligand properties.

Conclusions:

• Spacer ligand structure significantly impacts halide ion mobility and exchange mechanisms in 2D perovskites.
• The findings provide critical insights into controlling halide ion diffusion for tailored optoelectronic properties.
• This research lays the groundwork for designing advanced 2D perovskite materials with specific functionalities.