Stable Ultraconcentrated and Ultradilute Colloids of CsPbX₃ (X = Cl, Br) Nanocrystals Using Natural Lecithin as a Capping Ligand

Abstract

Attaining thermodynamic stability of colloids in a broad range of concentrations has long been a major thrust in the field of colloidal ligand-capped semiconductor nanocrystals (NCs). This challenge is particularly pressing for the novel NCs of cesium lead halide perovskites (CsPbX3; X = Cl, Br) owing to their highly dynamic and labile surfaces. Herein, we demonstrate that soy lecithin, a mass-produced natural phospholipid, serves as a tightly binding surface-capping ligand suited for a high-reaction yield synthesis of CsPbX3 NCs (6–10 nm) and allowing for long-term retention of the colloidal and structural integrity of CsPbX3 NCs in a broad range of concentrations—from a few ng/mL to >400 mg/mL (inorganic core mass). The high colloidal stability achieved with this long-chain zwitterionic ligand can be rationalized with the Alexander–De Gennes model that considers the increased particle–particle repulsion due to branched chains and ligand polydispersity. The versatility and immense practical utility of such colloids is showcased by the single NC spectroscopy on ultradilute samples and, conversely, by obtaining micrometer-thick, optically homogeneous dense NC films in a single spin-coating step from ultraconcentrated colloids.

Aromatic nonpolar organogels for efficient and stable perovskite green emitters

“…The color purity of the devices will be improved by reducing the transmission of excitation light. It can be achieved with more densely dispersed PNC-organogel nanocomposites, enabled by introducing more soluble PNCs to the organogel precursors, such as a kind of PNCs having longer or branched capping ligands 31 .…”

Lead Halide Perovskite Nanocrystals: Room Temperature Syntheses toward Commercial Viability

“…The same group took this a step further recently, utilizing soy lecithin as a ligand-a low-cost, mass-produced, zwitterionic phospholipid. [93] Soy lecithin contains a long polydisperse branched alkyl chain (see Figure 13), thus as discussed earlier, there will be little enthalpic driving force to pack the ligand chains together and a huge entropic barrier. [34,42] With this ligand, CsPbBr 3 NC inks with concentration ranging from ng mL −1 to >400 mg mL −1 were obtained; as a result, both isolated single NCs and thin films with thicknesses up to 1.5 µm were feasible.…”

“…This is in agreement with the enormous increase in colloidal stability obtained with very long, highly branched, soy lecithin. [93] However, this concept has not yet been explored for shorter chain ligands suitable for perovskite NC LEDs. There are many commercially available branched-chain carboxylic acids and amines, as well as recent reported syntheses of branched phosphonic acids.…”

Automated microfluidic screening of ligand interactions during the synthesis of cesium lead bromide nanocrystals

“…As a result, it is common to observe multiple peaks in the PL spectra of crude reaction solutions, arising from variable levels of quantum confinement in the different sized nanocrystals. 55 This often necessitates careful post-synthetic processing to isolate a monodisperse population, 32 with the purification procedure (typically using polar solvents) commonly leading to degradation of the ligand shell and therefore the nanocrystals. 56,57 When analysing spectral data, we report the dominant peak position, the median peak position, the peak intensity and the interquartile range (see Fig.…”

“…29 Further, although interpenetration of ligands on colliding nanocrystals can lead to particle aggregation due to attractive van der Waals forces, branched or unsaturated ligands can restrict this due to a disruption of ligand alignment. This effect has been explored by Krieg et al in their development of zwitterionic capping ligands for CsPbX 3 nanocrystal synthesis, 32,33 and by Yang et al in studying the colloidal stability of CdSe nanocrystals with n-alkanoate ligands. 34,35 It is important to note that large scale screening and mapping of reaction parameter spaces in the synthesis of LHP nanocrystals is hindered by the low throughput of traditional flask-based synthetic approaches.…”