Surface Structure of Lecithin-Capped Cesium Lead Halide Perovskite Nanocrystals Using Solid-State and Dynamic Nuclear...

Area of Science:

• Materials Science
• Nanotechnology
• Solid-State Chemistry

Background:

• Inorganic colloidal cesium lead halide perovskite nanocrystals (NCs) are crucial for optoelectronic applications.
• Surface capping ligands significantly influence the photophysical properties of NCs.
• Soy lecithin has enabled high-yield synthesis of stable CsPbX₃ NC colloids, but its surface interaction is unclear.

Purpose of the Study:

• To elucidate the atomic-level surface structure of CsPbX₃ NCs capped with soy lecithin.
• To understand the interaction between lecithin head-groups and the perovskite NC surface.
• To provide insights for engineering surface ligands for metal halide perovskites.

Main Methods:

• Solid-state nuclear magnetic resonance (NMR) spectroscopy, including dynamic nuclear polarization (DNP) enhanced NMR.
• Surface-selective NMR techniques (e.g., cross-polarization, rotational-echo double-resonance).
• Atomistic molecular dynamics (MD) simulations.

Main Results:

• NMR and DNP experiments differentiated surface and core chemical environments of CsPbX₃ NCs.
• Lecithin's trimethylammonium and phosphate head-groups were assigned using various NMR nuclei (¹H, ¹³C, ³¹P).
• Direct evidence of trimethylammonium binding to surface/subsurface Cs and phosphate binding to subsurface Pb was obtained.
• MD simulations suggest lecithin head-groups substitute surface Cs⁺ and Cl⁻ ions.

Conclusions:

• Soy lecithin acts as a zwitterionic ligand, with its head-groups directly interacting with the CsPbCl₃ NC surface.
• The trimethylammonium and phosphate groups substitute for Cs⁺ and Cl⁻ ions, respectively, at the CsCl-terminated surface.
• These findings offer detailed atomistic understanding to guide future ligand design for perovskite NCs.