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.