Highly Dynamic Ligand Binding and Light Absorption Coefficient of Cesium Lead Bromide Perovskite Nanocrystals

TLDR

Lead halide perovskite nanocrystals, especially CsPbX3, are promising for optoelectronics due to tunable bright photoluminescence, yet their surface chemistry and quantitative light absorption remain poorly understood. This study aims to detail the synthesis of CsPbBr3 nanocrystals and investigate their surface chemistry. We synthesized CsPbBr3 nanocrystals, characterized their surface chemistry and purity by 1H NMR, and experimentally measured the intrinsic absorption coefficient using elemental analysis combined with optical absorption. Ligand binding is highly dynamic, causing ligand loss during purification, but adding small amounts of oleic acid and oleylamine preserves colloidal and optical integrity, and a higher amine content in the ligand shell boosts quantum yield by strengthening carboxylic acid binding.

Abstract

Lead halide perovskite materials have attracted significant attention in the context of photovoltaics and other optoelectronic applications, and recently, research efforts have been directed to nanostructured lead halide perovskites. Collodial nanocrystals (NCs) of cesium lead halides (CsPbX3, X = Cl, Br, I) exhibit bright photoluminescence, with emission tunable over the entire visible spectral region. However, previous studies on CsPbX3 NCs did not address key aspects of their chemistry and photophysics such as surface chemistry and quantitative light absorption. Here, we elaborate on the synthesis of CsPbBr3 NCs and their surface chemistry. In addition, the intrinsic absorption coefficient was determined experimentally by combining elemental analysis with accurate optical absorption measurements. 1H solution nuclear magnetic resonance spectroscopy was used to characterize sample purity, elucidate the surface chemistry, and evaluate the influence of purification methods on the surface composition. We find that ligand binding to the NC surface is highly dynamic, and therefore, ligands are easily lost during the isolation and purification procedures. However, when a small amount of both oleic acid and oleylamine is added, the NCs can be purified, maintaining optical, colloidal, and material integrity. In addition, we find that a high amine content in the ligand shell increases the quantum yield due to the improved binding of the carboxylic acid.