Ligand-Controlled Phonon Dynamics in CsPbBr₃ Nanocrystals Revealed by Machine-Learned Interatomic Potentials

Area of Science:

• Materials Science
• Nanotechnology
• Solid-State Physics

Background:

• Halide perovskite nanocrystals are promising for advanced optoelectronics.
• Surface ligands critically influence nanocrystal properties, including phonon dynamics.
• Understanding ligand effects on phonon behavior is vital for device efficiency.

Purpose of the Study:

• To investigate the role of surface ligands in controlling phonon dynamics of halide perovskite nanocrystals.
• To develop accurate computational methods for studying ligand-induced phonon properties at experimentally relevant scales.
• To provide mechanistic insights into ligand modulation of lattice vibrations for improved optoelectronic applications.

Main Methods:

• Development of a machine-learned interatomic potential.
• Fine-tuning the potential on small CsPbBr₃ nanocrystals with diverse ligands.
• Simulations beyond the scale of conventional ab initio methods.

Main Results:

• Both cationic and anionic ligands redshift Pb-Br-Pb stretching modes.
• Anionic ligands blueshift the PbBr₆ ^4- octahedral rotation mode, with nonmonotonic stiffening.
• Ligand effects are site-dependent, with corner and edge sites showing the largest response.

Conclusions:

• Surface ligands play a crucial role in modulating phonon modes in halide perovskite nanocrystals.
• Ligand engineering can tune lattice dynamics to minimize nonradiative losses.
• Findings offer design principles for high-performance perovskite nanocrystal optoelectronics.